The Hardy boys hurried back to tell the director the bottle of pollen was missing. The man was not unduly disturbed.
"Probably the clerk put it on the wrong shelf. Or maybe someone needed the sample in a hurry and the clerk was off duty at the time, so the bottle went out without being entered in the records. I have some of the stuff in my private office, anyhow. Come along and I'll let you have some of it."
On the way Frank ventured an inquiry about Boots.
"An interesting character," he remarked innocently. "We were working with him the first day we came here."
"Oh yes–Boots. Very interesting fellow," said the director. ''He was hired by us, because he knows a good deal about rice culture, and the information was valuable to us in our underwater farming."
"Where did he learn about rice?" asked Joe.
"He was shipwrecked on an island somewhere in the Orient, I believe. He's had quite a history. Bather gruff in his manner, but he's a good workman and honest."
The Hardy boys were a little surprised by this high recommendation of Boots. As they waited for the director to locate the bottle, a figure passed beneath one of the open office windows. The fellow had been lurking there and had heard the entire conversation.
"Those two boys are gettin' awful smart," he muttered as he went off.
"Here you are, my boy. Here's the horrible African lily pollen," smiled the director, coming back with a tiny vial. ''Don't let any of it get on your clothes, or you'll both be as unpopular as a pair of polecats!''
Smiling, the boys thanked him and promised to take good care of the rare stuff. They were glad, nevertheless, that the director did not ask them why they wanted it.
"Just as soon as we finish work this afternoon," resolved Frank, "we'll look up O'Brien and find out if this is what he smelled last night. And if it is–"
"If it is," Joe declared, "I think we'll have a first-rate clue to that robbery. With Mr. Boots right in the middle of it, I don't care what the director says about him."
When their day's work was over, the boys went directly to the garage where they had left their car to be repaired. They arrived, fully expecting that they would drive it away at once. The young mechanic in charge of the place at the moment astounded them by saying:
''Your car? It went out an hour ago.''
"Went out?" exclaimed Frank. "Why was that? We gave no one permission to use it."
"But you sent your sister for it, didn't you? She came here and picked up the car. Said you told her to call for it.''
The Hardy boys were astounded.
" Sister!" cried Joe. "That's the first I've heard about her. We haven't a sister."
Now the mechanic was worried. ''Gee whiz!'' he exclaimed. ''Do you mean to tell me I turned that car over to the wrong person? The girl said she was your sister. She was so cool about it, I didn't dream there was anything wrong. Oh, my boss will certainly fire me for this!"
The Hardy boys pressed him for a description of the "sister" who had claimed their automobile. The fellow said he had not noticed her particularly.
''She had on a large hat with a veil, and had a rather deep voice, for a girl," he remembered. "Walked with a long stride. She paid for the repairs, and seemed to know all about the car, so naturally I thought it was all right.'' He indicated tire tracks in the dirt road. ''There are the tracks of the car."
The Hardy boys decided to follow them, so they hurried back to the Experimental Farm to borrow two horses. They found it easy to distinguish the tire marks, for there had been very little traffic on the dirt road since the stolen automobile had been driven off. But when the trail reached a paved highway, it vanished utterly.
"I have an idea about that 'sister' of ours," muttered Frank darkly. "From what the mechanic said, I think 'she' was not a girl at all."
"A boy in girl's clothes!"
Frank nodded. "It's all part of the mystery. We'd better report the stolen car to the police."
They rode quickly to Mrs. Trumper's. The widow groaned with dismay when they told her of the loss of their automobile.
"I never did know of such a run of bad luck. First your house burns, and now your car gets stolen!"
"The house didn't burn down, anyway, and maybe we'll get the car back," said Frank cheerfully.
He telephoned the Bayport police office and reported the loss of the car. The desk sergeant assured him the description and number of the automobile would be flashed to the state police and to other communities at once. There was nothing more the boys could do but wait and hope for the best.
"Here's a note that came for you about a quarter of an hour ago," Mrs. Trumper said. "Hearing about your ear made me forget about it. I hope it isn't more bad news."
She handed Joe a folded slip of paper. He opened it and read aloud:
"IF YOU WILL COME TO THE UNDERWATER SECTION AT ELEVEN O'CLOCK TONIGHT, I'LL TELL YOU WHO TOOK THE SAMPLE BOTTLE OF THE AFRICAN LILY POLLEN. AND I'LL HELP YOU CATCH THE THIEF WHO STOLE IT.
SAMPLE ROOM CLERK, S. E. F."
Joe turned the strange missive over. Nothing else was written on it. There was no name, no address, no further signature.
"What do you think of it?" he asked Frank doubtfully.
"I don't like it." His brother studied the note. "I think it's a hoax."
"On the other hand, if it isn't a hoax, maybe we'd miss something important if we don't go."
Frank thought for a moment. ''Our best plan is to find out more about that sample room clerk. He probably rooms in the village, like most of the Farm employees. Let's check up on him."
They said good-by to Mrs. Trumper who warned them to be careful. On horseback the boys clattered out of the lane and down the country road to the village. A boy in the ice cream parlor was able to tell them about the sample room clerk at the State Experimental Farm.
"Sure," said the lad, "that's George Gilman. But you won't find him for a while. He took his girl to Bayport to a movie."
"You don't happen to know when he might get back, do you?'' asked Frank.
" I heard her tell him she had to be home by ten-thirty," grinned the boy. "And he said that was all right by him, 'cause he had another date at eleven o 'clock.''
The Hardys heard no more. They looked at each other knowingly, thanked the boy, and left.
"Well, I guess we show up at the S. E. F. at eleven o'clock," said Joe in a whisper. "Say, look!"
There was a cheap restaurant across the street. Through the front window the boys could see the white-topped tables. At one of them two men were seated, leaning forward in earnest conversation.
Joe whistled. "So those two know each other!" he exclaimed shortly.
The Hardy boys had good reason to be surprised. For the men were Boots and Hefty Cronin.
The Hardy boys remained where they were, watching. After a while Boots got up and left the restaurant. Hefty Cronin sat idly at the table for a few minutes, then he too arose and left the place. Boots shambled off down the street. Cronin climbed into a truck parked near by and drove away.
"I'd give a lot to know what those two were talking about," remarked Frank.
"I'd give a lot to know what's going to happen when we show up for that date at eleven o'clock!"
They were still inclined to believe it might be a trap. In this case they would enter it with their eyes open. This might even turn out to be an opportunity to come to grips with hidden enemies.
A few minutes before eleven o'clock that night the two Hardys on horseback rode slowly into the grounds of the Experimental Farm. The place seemed deserted. By night the paths lay in eerie shadows. In the underwater section the air was filled with the odor of the swampy tanks where Boots grew his weeds and plants. The atmosphere was sinister and uncanny.
The boys drew their horses to a stop. Already they had planned a course of action. To guard against surprise, they had arranged to face their horses in opposite directions, so that each boy, high in the saddle, could scan a different part of the grounds. Any one approaching by the path, thus would not be able to steal up on them unobserved.
But the Hardy boys had reckoned without the crafty wits behind the note that had lured them to the place. Both of them knew about the high platform above the tanks. They had seen it often in their work around the Farm. It loomed just above the level of their shoulders, a dark oblong shadow in the night.
So absorbed were they in watching the ground that neither of them saw the first slight movement on the platform. Slowly a head was raised–a head without face or features–a head grimly hooded, with eyes that peered through ragged slits in the rough cloth.
Then another hooded head appeared. The figures arose, crouching, gazing malignantly at the boys below them. There was a silent signal. Both figures launched themselves suddenly from the platform. They flung their robes over the boys, hurling them from their saddles!
CHAPTER XIX
AUNT GERTRUDE STEPS IN
The Hardy boys were taken completely by surprise!
They had been in and out of so many tight fixes in the course of their adventures as amateur detectives that by this time, they had come to pride themselves on their ability to look ahead and to guard against traps. And this was a trap they had entered with their eyes open. In spite of all their caution, they had been outwitted.
The boys struggled furiously. Enveloped in the heavy folds of the cloaks, they were almost helpless. The two hooded figures overpowered them easily. The frightened horses, after rearing and plunging in terror, suddenly bolted and raced off down the path in the direction of the distant stables.
Muffled by the heavy cloth, the boys' shouts did not carry more than a few yards away. At that hour of night the grounds of the Experimental Farm were deserted. Frank and Joe, still fighting, were bound with ropes and dragged off down the path and through a clump of bushes. In a driveway near at hand a car was parked beneath some trees.
One of the hooded figures wrenched open the door. The boys were bundled into the back seat. The other man slid behind the wheel, while his companion jumped in and stood guard over the boys. The automobile leaped forward, its lights dimmed.
Frank knew that struggle was useless. They had walked right into a trap, and he bitterly realized that they should have been smart enough to have avoided it. As the car sped through the night, he set his mind to estimating the length of the journey, and to trying to ascertain the direction the car was taking. It veered to the right, stayed on a rough road for a few minutes, then made a wide swing to the left. Presently it struck a smooth stretch of roadway, continued on this for about a hundred yards, swung to the right again. It ran along a rough, bumpy surface, and finally slid to a stop.
"I could almost believe we've been going in circles," thought Frank.
The boys were lifted from the car. They were dragged and pushed through a doorway, then given violent shoves. A door thudded shut. They heard a mocking laugh and then the echoes of footsteps as the men hurried away.
"Joe!" Frank called out through the stifling folds of the hood. "Are you here, Joe?"
A muffled shout indicated that his brother had been thrown into the same prison. Frank worked furiously at the ropes. They had been hastily tied, and in a few minutes he managed to wriggle free. He wrenched at the hood and worked it clear of his head.
He could see nothing. The place was in utter darkness. Near by he could hear Joe grunting and panting in his efforts to extricate himself. Frank groped his way through the darkness to his brother's side. He tugged at the ropes and soon the other boy was free.
"Where are we?" gasped Joe, getting to his feet.
"In the dark, and that's all I can tell. A fine pair of detectives we are!" Frank grumbled with disgust. "Letting ourselves be caught!"
"Stuck our heads right into the trap like a couple rabbits!" Joe groaned.
He felt in his pockets, and finally discovered a match. Then he groped his way forward, until his outstretched hand came in contact with a concrete wall. He lit the match.
Its meager flame revealed that they were in a small, square room, with concrete floor and walls. There were no windows-only a ventilator set high in one wall, close to the ceiling. The heavy wooden door was locked.
"We're in a tough spot!" muttered Joe, worried. The match burned down and flickered out, "If those fellows don't come back and let us out, we may starve to death.''
"Here's another match," said Frank. The flame blazed up. "I thought I saw something over there."
By the tiny light Frank investigated. In one corner of their prison he found a box. Evidently it had been left there for them, as it contained several loaves of bread, a large bottle of water, cold meat and cheese-enough food to last them a week.
"Well," said Frank, relieved, "at least they don't mean to starve us. But from the quantity of food, I figure they intend to leave us here for a few days."
"And what's going to happen in those few days?" remarked Joe.
The brothers realized now that the conspirators had set another trap similar to the first one. If the fire at the Hardy home had been meant to keep the boys out of the way, this trap had the same purpose.
"That ventilator is pretty high up. But maybe one of us could reach it." Joe took up a position against the wall. "Try climbing up on my shoulders."
Frank's match flickered out. He felt his way across the room, put his foot in Joe's cupped hands, and managed to scramble up. He pulled himself up high enough to see through the ventilator. There was nothing but pitch darkness, although he could detect rain. He even thought he could scent a faint odor of flowers.
"I think we're still on the Experimental Farm property," he said as he leaped to the floor. ''Remember those concrete storage houses we saw on our first day here? I have an idea we're locked in one of them."
"The storage places are in a field at the far end of the farm. Nobody ever comes near them. We could shout ourselves hoarse and we'd never be heard."
"That," said Frank, "is probably why the men in the hoods brought us here." Gloomily he sat down on the floor with his back against the wall. "No use fooling ourselves, Joe. We've been neatly tricked, and I think we're going to be here for a long, long time."
The boys stared into the darkness. They wondered how much time would elapse before they would be missed. There would be a search, of course. But who would think of looking in the old storage vaults?
"Aunt Gertrude will say it serves us right for falling into such a simple trap," groaned Joe. "She'll say anyone should have known that message was a fake."
And in this Joe was right. That, in fact, was exactly what Aunt Gertrude did say after she returned to Mrs. Trumper's farmhouse the next morning. Their relative had not come there to stay. Because of the fire, the Hardy home was undergoing repairs, and she felt that her services were urgently needed to supervise these operations.
But when she had opened the bag she had packed so hastily when she had left Mrs. Trumper's, she made a discovery. In her excitement, Aunt Gertrude had packed a considerable quantity of the widow's personal papers. She had been giving them some study, hoping to prove her belief that Hal Wortman had cheated the shy little woman when he bought some of her farm acreage.
Aunt Gertrude realized that the papers must be returned, so she journeyed back to the widow's house that morning from Bayport. It was then that she learned her nephews were still away.
"Staying out all night, eh!" sniffed the boys' relative. "Up to more of their silly detective work, I'll be bound." Actually Aunt Gertrude did not consider detective work silly. She was secretly proud of her nephews' achievements in that line.
For some time she expected them to show up any minute, but as the morning wore into noon and no word came from them, she became disturbed. She telephoned to the S. E. F. and to Mr. Grable. Frank and Joe had not been seen.
"What in the world can have become of them?" fumed Aunt Gertrude.
"A note came for them yesterday. I have it here," said Mrs. Trumper. "As soon as the boys read it, they went away."
''Let me see that note!'' Aunt Gertrude read the crumpled missive with rising suspicion. Then she snorted. "A fake!" she declared. "A transparent fake. They've been kidnaped!" she shrieked, heading for the telephone. "Fenton must hear of this at once!"
"Do you really think they've run into some danger?" quavered the widow anxiously.
Aunt Gertrude rattled the receiver impatiently. When the village central office answered, she put through a call for the Hardy residence in Bayport. "And don't dawdle, young lady," she said to the operator. "This is a matter of life and death!"
The widow was aghast. "Life and death!" she moaned. ''Oh, my goodness!''
The connection was put through quickly. When Aunt Gertrude heard her brother's voice on the wire she was relieved.
"I'm so glad I caught you, Fenton. You'd better come out here as fast as you can. Frank and Joe have disappeared and it's my opinion they've walked into a trap."
"You say they've disappeared?" exclaimed Fenton Hardy.
"Yes, but don't tell Laura. She'll worry herself sick. I'll help you find the boys, but hurry out here!"
"I'll start this minute!" promised Fenton Hardy. The receiver clicked.
The boys' father returned to his living room, where he had been in conference with a private detective named Walter Cartwright. Mr. Hardy occasionally employed this man on some of his more complicated cases. Cartwright had just arrived in Bayport from New York.
"Come along," said the boys' father. "I'll probably need you. My sons have disappeared."
Fenton Hardy seldom displayed excitement or emotion, but his face was pale as he hurried out of the house and into his car. Cartwright scrambled in beside him. As they drove swiftly through Bayport and out the country road to the Trumper homestead, the troubled man outlined the brief details Aunt Gertrude had told him.
Cartwright whistled. "Maybe the boys stumbled on something big. If they've become tangled with the flickering torch gang, it may be serious," he said.
"We'll hope for the best," returned Fenton Hardy gravely. "They're a resourceful pair. They've been in some pretty tight spots before this."
When the detectives saw the note from the S. B. F. sample room clerk, they agreed with Aunt Gertrude that it probably was a fake. Nevertheless, Fenton Hardy stepped to the telephone and called the storeroom department at the Experimental Farm, and asked to speak to the young man in charge.
"Certainly, I remember the boys," the clerk said in reply to his question. "Write them a note! Why should I write them any note! As for asking them to meet me at the underwater section-somebody must have been playing a practical joke."
Fenton Hardy checked up on the man and found he had been nowhere near the S. E. F. at eleven o'clock the evening before. That settled it. He and Cartwright got into the car. The obvious place to begin their search was at the underwater section where the boys were presumed to have kept their strange appointment the previous night.
"I'm going along," declared Aunt Gertrude. "I won't rest easy until I see those boys again. And if they've been mistreated, they'll need me."
Mr. Hardy did not argue with his sister. He was in too much of a hurry, so he waited only long enough for her to step into the back of the car. Then he set out for the spot from where he would try to trace his boys. The rain had filled the holes of the hoofmarks left by the horses the boys had ridden the night before. But these ended in the S. E. F. stables. Every other clue had been washed away.
"I'm afraid we're up against a difficult proposition," whispered Mr. Hardy to Cartwright, a slight catch in his voice.
CHAPTER XX
THE BOTTOMLESS POOL
Frank and Joe, knowing there was no chance to escape from their prison during the night, finally had spread the black hooded robes on the floor, and gone to sleep on them. But as soon as it was light, they looked through the ventilator again, confirming their suspicion that they were on the Experimental Farm in a storage room not in use at present.
"So no one is likely to come near here," groaned Joe.
Nevertheless, as soon as they knew the workers would be arriving on the place, the boys took turns shouting through the opening high overhead. There was no response.
"Let's eat," suggested Frank, "and try to figure this thing out. What's your idea of who brought us here last night?"
"Boots, for one. Who else would have thought about using that platform at the underwater farming section? But I can't be sure of the other man."
"How about Cronin? You recall he and Boots acted in that Midvale restaurant as if they were making plans for something."
"We got the note before that," objected Joe.
"True, but probably they were only rehearsing a scheme already made," replied Frank. "What puzzles me is why they left these robes."
"There's no identifying mark on them," said Joe. "And if our guess is correct, that they intend to keep us here for several days, the flickering torch gang will have pulled their big job and skipped out. Knowing that Dad and we are onto their disguise, they'll probably never use it after this time."
Frank suddenly slapped his knee. "I just thought of something!" he exclaimed. "You remember that boy on the cliff-the one Chet and I thought was you? I'll bet he's part of the gang. When the hooded man drew him inside his cloak, it was a signal!"
"A signal for what?"
"An order for the men to capture a boy who was sneaking up on them. That would mean you or me."
"It's a good hunch," praised his brother. "And that boy probably is the one who posed as our 'sister' and stole our-Listen!"
Joe thought he heard footsteps outside. Was one of their captors coming back or was help arriving?
"Quick! Let me jump on your shoulders and look out the ventilator!" he said excitedly.
But when he gazed through the opening, he could neither see nor hear anyone. Hours passed, the Hardy boys becoming more vexed as time went on.
The boys had just finished eating a second meal when they became aware of a car passing near by. In an instant Frank had jumped to Joe's shoulders and was shouting through the ventilator. Already the automobile was some distance away. Would the driver hear him?
"Joe," his brother cried excitedly, "that was Dad's car! Help! Help! Dad!"
The car did not even slow down, but a few moments later a lady in the back seat of it grasped a shoulder of the man in front of her and ordered him to stop.
"I'm sure I heard a cry for help," she said. "It might be the boys, Fenton."
"I'll turn around, Gertrude," the driver said, "but I didn't hear anything. Did you, Cartwright?"
"No, but–"
''Help! Help!'' came a distant cry.
"It's the boys! I knew it!" shouted Aunt Gertrude triumphantly. ''That's Frank's voice. I'd know it anywhere."
Fenton Hardy hurried toward the sound. "In the middle storage room," he decided.
In a few moments they could see Frank's face through the ventilator.
"Are you all right?" cried Aunt Gertrude.
"Yes. Gee, we're glad to see you."
His aunt began to ask questions, while his father and the other detective tried to open the door to the building.
"It's no use. I'll go to the Farm office and get a key," volunteered Cartwright.
While he was away, the others carried on a two-way conversation through the ventilator.
"You can thank your aunt for your rescue," said Fenton Hardy. '' She suspected that note the moment she read it! And now I would have gone right past you. I was following a clue to your stolen car. Thought maybe you'd been taken away in it."
"We might have been at that," said Joe, who was taking a turn at speaking. "Was any big robbery pulled off last night?"
"No. Whatever the flickering torch gang has in mind, it hasn't happened yet. Well, here comes the key."
The S. E. F. Director was with Cartwright. He was very much upset about what had happened, and asked the boys many questions as he let them out.
"We suspect Boots," said Frank. "Where is he?"
"He didn't report for work this morning," the man told him.
The Hardys and Cartwright had agreed not to tell the director anything about the flickering torch gang, as he might let a word drop which would upset their sleuthing in the case. He felt, and they did not disabuse his mind, that it was entirely a personal animosity of Boots toward the boys.
"I know he didn't seem to like you two, but I didn't think he'd resort to kidnaping to prevent your working here," he said. "By the way, if you're not too tired, I wish you'd lend a hand at the underwater section. Without Boots–"
The boys looked at their father. ''Go ahead,'' he said. "I'll see you later." Aside he added in a low tone, "I'll do some investigating this afternoon, and tonight we'll lay plans. I think you boys have made more headway on this case than you imagine."
That compliment to the boys spurred them on in their work in the underwater section. They did not fancy doing the chores of the absent Boots, but they looked forward to catching him later.
Finally work was over for the day. As the boys were about to start for home, the director came to speak to them.
"Your Dad phoned that he checked on Boots,'' he said. ''The man has left his boarding house and given no forwarding address."
Apparently Boots had cleared out. Had he taken alarm and fled before the net closed about him?
The boys trudged off toward Mrs. Trumper's.
"What say to a swim?" decided Frank. "You know that pool between here and home?"
The deep dark pool, shaded by huge trees, was just off the property line of the Experimental Farm. The boys had passed it a number of times on their way to and from work when they crossed the fields. It had seemed odd to them that they never had seen any of the village boys swimming there.
"That ought to be the most popular swimming pole in the neighborhood," said Joe as they crossed the meadows. "It seems like an ideal spot."
The sides of the pool were steep and rocky. The water was so black that the brothers realized it must be very deep. They stripped off their clothes and went in. The sides of the pool dropped straight down.
The place was perfect for diving. Splashing and laughing in the cold water, the boys enjoyed their dip immensely.
"Although I must say," gasped Joe, "this water is so cold there must be ice at the bottom."
"I'm wondering if there is any bottom," said Frank. He poised himself for a dive, and went straight down as far as he could go. But his groping fingers encountered no bottom to the pool. He emerged, gasping. "I don't think this is a pool at all. It's a bottomless pit!"
Its depth had given the boy an idea. Hurriedly he began scrambling into his clothes.
"Maybe I'm wrong," he said mysteriously, "but I have a hunch. Get dressed and come along.''
"Where to?"
"To Mrs. Trumper's. She knows all about this neighborhood. If there's any story connected with this pool, she's bound to know it."
There was a story connected with the pool. As Frank had guessed, the Widow Trumper did know about it. She was quite bewildered when the Hardys rushed into the house, asking her to tell them about the spot.
"That!" exclaimed the widow. "That's no swimming pool. My goodness, don't tell me you boys went swimming there. You might have drowned. I intended to warn you about that place." She turned pale at the thought of what might have happened, and began fanning herself with a newspaper. "Dear me, it makes me quite faint to think of it. Last night you were kidnaped, your aunt told me–she's gone home again, by the way–and today you nearly drown!"
"Well, we're home safe and sound," Frank assured her. ''But how about the pool? Why is it so dangerous?"
"Because it's hundreds of feet deep, that's why," declared the widow. "It's a mine pit. There used to be iron mines around here, way back in the days of the American Revolution.''
" A mine shaft!" Frank snapped his fingers in excitement, and motioned to his brother to follow him upstairs. "Why didn't I think of that before?" he added in the privacy of their room. "It's the very clue we've been waiting for."
"Tell me," said Joe eagerly.
"Don't you see?" cried Frank. "If there's a mine pit, there is also a mine. Perhaps the shaft to it is under Wortman's cottage. Maybe this will explain a whole lot of things that have been bothering us. Eemember how Wortman went down into his cellar? Perhaps that is the place where Boots is hiding!"
CHAPTER XXI
UNDERGROUND
Joe whistled at Frank's astounding theory that an old mine beneath them had an opening under Wortman's cottage.
"I think you have something, Frank. What a wonderful place to hide stolen property! And that earthquake! Maybe it wasn't an earthquake at all-just blasting underground to make more room!"
"We're going to watch Wortman's place tonight. I wish we could be at Grable's, too," said Frank. "But the other seems more important now."
The boys telephoned home, hoping to find out where their father was, but the family had not heard from him. They left word telling where they were going, and also told this to Mrs. Trumper.
"Take care of yourselves," she said solicitously. "Don't let anyone kidnap you again."
It was almost dark when they crossed the fields behind Mrs. Trumper's house. They reached the path to Hal Wortman's. A truck was just turning in from the highway. It rolled up the lane and disappeared behind the cottage.
The boys hesitated, uncertain whether to go on or not.
"The driver might be Wortman himself. We don't want him to catch us hanging around," Joe cautioned.
"We'll wait a few minutes and see what happens."
Nothing happened, beyond the fact that the truck backed out from behind the house a moment later, turned in the yard, and rolled off down the lane as quickly as it had come.
"No lights in the cottage," whispered Frank as the boys crawled over the fence. "But that doesn't mean anything, if I'm right in my underground theory."
They crept forward. Suddenly they heard a creaking noise, and saw a figure coming from the building. The brothers huddled motionless in the shadows, and watched.
The person who had emerged was a boy of about their own age. In the darkness they could not see his face, but the Hardys were sure they had never seen him before. The moment he had disappeared, Frank nudged his brother, then leaped silently forward and crossed the yard at a run.
"This is our chance to get inside!" he whispered.
The trap door was open. At the foot of the stairs was a dim electric light. Quickly the Hardys groped their way down the steps.
A tunnel lay before them. It was well lighted. In the distance they could hear a steady sound of tapping.
Presently they came to a wooden platform and another series of steps. They descended the stairs and found themselves in a long passage that had been excavated out of the rock.
"Wortman's cottage wasn't, so innocent after all," whispered Frank.
His voice echoed sibilantly from the rocky walls. Far behind them they heard a sharp thud. Then footsteps.
''The boy!'' said Joe tensely in a low voice. "He's coming back."
There was no place to hide!
As quietly and quickly as they could, the Hardys went on deeper into the rocky corridor. The distant tapping was louder now. The footsteps on the stairs continued. They were catching up. The brothers could not turn back. And the tapping warned them that someone was in the passageway ahead.
"I guess we're caught!" whispered Joe.
Then Frank spied a door just around a bend. He sprang toward it, flung it open, pushed Joe inside, and scrambled in himself. He closed the door just before the person reached the turn.
The Hardy boys were wedged in a small closet. Breathlessly, they waited in the darkness, listening. Perhaps they had been seen! This closet might prove to be a trap instead of a hiding place!
The footsteps echoed loudly in the passageway. They came closer to the closet door, slowed down a moment-and then went on. Finally they died away.
''Whew!'' breathed Frank in relief. ''That was a close one!''
Slowly he opened the door. The Hardys peeped out. The place was deserted. Down the way they saw the boy. But he was going away from them, apparently quite without suspicion that anyone had entered the place in the few minutes he had spent outside Wortman's cottage.
The lights strung along the corridor illuminated the interior of the closet in which the boys had hidden themselves. Hanging from a hook on the wall were two long garments. Joe reached up and took down one of them.
It was a long black cloak with a hood!
Now at last, the Hardy boys knew they had found the retreat of the hooded men-at least some of them.
"Let's take these along. They may come in handy," suggested Frank. "And I guess it's safe to go on now."
"With the black robes over their arms, they tiptoed forward. Coming to a tunnel that adjoined the one they were in, Joe stopped short. The place was in darkness, so the boy turned his flashlight into the interior. He gave a gasp of astonishment.
"The loot!" he whispered hoarsely.
The tunnel was so long they could not see the end of it. Each wall was lined to the ceiling with boxes. From the markings on them the boys knew they contained stolen goods.
"And here's more proof!" whispered Frank suddenly. He picked up a torch handle identical with those found at Grable's and outside the Hardy home. "I'm sure now this is the headquarters of the flickering torch gang!" the boy said firmly.
"But where does Asa Grable fit in?" asked Joe. " Is he or isn't he one of them?"
Frank had no answer. Instead, he remarked, "Won't Dad be thrilled to learn about this stuff?"
"Yes," said Joe. "But, after all, it's more important to find the thieves."
"We haven't found one of the gang yet!"
"Let's go on to the–"
Suddenly they heard footsteps in the main passageway. In the glow of the electric lights they saw a man trudging straight toward them. He was about fifty yards away, and under his arm he carried a bulky object. It looked, to the Hardy boys, like a machine gun!
If the man was coming into the storeroom tunnel with his burden, the boys surely would be seen! The fellow advanced steadily, his eyes turned on the opening.
CHAPTER XXII
THE HIDDEN DOOR
The boys looked frantically for a hiding place. There was none. They pressed themselves against the boxes. The footsteps became louder.
Then the man walked past. After he trudged by, the Hardys sighed in relief.
"Another close call like that, and I'll be a nervous wreck," murmured Joe.
"Did you notice what he was carrying?"
"I thought it was a machine gun."
Frank shook his head. "That's what I thought at first. But it wasn't. I got a good look at it when he went by. It was a power drill."
"Like the one we found in the scarecrow?"
"Exactly like it. Maybe the same one. I think–"
"Sh-h! Listen!"
Off down the passageway they heard more footsteps. The fellow with the power drill had gone up the stairs into the upper part of the shaft. But now someone else was approaching. They heard the voices of two men, echoing in the rocky passage.
Hardly daring to breathe, the boys crouched in their hiding place and waited. The men drew closer, then stopped at the entrance to the tunnel. They were pushing a cart, which seemed to be heavy.
The brothers wondered if the men had caught a glimpse of them. But apparently they merely halted to rest a moment. In the cart were several large pieces of pale blue rock.
"Nice stuff," one of the workmen said.
"I wonder if the old timers who dug iron ore out of this mine knew about it," remarked the other.
''Back in Revolutionary days they never even dreamed of cobalastium. It's a lot more valuable than iron."
"Especially now. The government is trying to round up a lot of it. Well–let's go.''
They put the ore back in the cart and went on. Presently they disappeared.
"This mine is being worked, but not for iron," said Joe quietly. "Whatever those fellows are doing with it, they keep it a secret. Let's go on a little farther and find out what we can."
A few moments later they could see miners at work, drilling in the rock wall. The boys dared go no closer. Curious, they decided to investigate a narrow tunnel, branching off the main passageway. It was dark. Frank took a flashlight from his pocket and switched it on.
The beam revealed grim, rough-hewn walls vanishing into blackness.
"Look!" whispered Joe. "A pile of torch handles!"
These were stacked on a small ledge at one side of the corridor. There were several dozen of them.
"Maybe we'd better take along a couple. They may come in handy," advised Frank.
The brothers each took one, then hurried through the tunnel. It continued on and on, winding underground. The floor was deep in dust and soot. In it were human footprints. The boys crouched and examined them.
"Looks as if this channel is used, even if it isn't lighted," Frank remarked.
''But only by one person!'' Joe had his own flashlight out now and was scrutinizing the footprints closely. "Don't you see-they're all alike. All the same size, coming and going. And they are all certainly made by the same pair of shoes."
Mystified, the boys followed the tunnel farther. Here and there in the walls they found places where holes had been bored. For a time these puzzled them, until at last they came to a torch handle, projecting from the rocks.
"I'm beginning to see through this torch business," Frank said. "In the olden days, when this mine was originally worked, the passages were lighted by torches. Probably they held pine pitch. That explains the pile of han dies we've found."
"I'm beginning to have a few ideas about the ones in Asa Grable's laboratory," remarked Joe. "Do you know what I think? This tunnel leads under the Grable property.''
''You may be right. It runs in that direction. And the Wortman cottage isn't far from Grable's place."
Frank hurried on. Joe's suggestion filled him with excitement. The existence of the passage might be the solution to a great many things. It might explain, for instance, how thieves got into the Grable greenhouses without setting off the burglar alarm. He mentioned this to Joe.
"But what would the flickering torch gang want with silkworms?" Joe objected.
"If I could answer that, the whole mystery would be solved. But I think we're going to find out," declared Frank.
They stumbled on down the dusty old tunnel. At last it came to an end-but not to another passage; not in any subterranean chamber; not in any shaft leading to the outside world. It simply came to an end, sloping sharply and narrowing down until it was only a few feet wide.
''That's strange,'' Frank muttered. ''Footprints in the dust, so somebody has used this passage. But it doesn't lead anywhere."
He turned his flashlight full on the end of the tunnel. A pile of rocks, one on top of the other, blocked any further progress. Frank stepped forward and pulled at the rocks with all his strength.
To his astonishment they moved. There was a dismal creaking of hinges. The rocks suddenly moved toward him, then swung to one side. A door opened as if by magic.
Joe whistled. "Pretty neat!" he exclaimed.
The wooden door had a projecting base on each side. On these, rocks were piled up. Thus it could be closed from either side without disturbing the rocks, which apparently were there to hide the door from view.
Cautiously, the Hardy boys passed through the strange entrance. The flashlights showed them a heavy wooden barrier a few feet away. Frank grasped the knob, tried to open it.
It was locked.
What mystery lay behind that locked door? Perhaps it guarded the secret to all the strange events that had puzzled them.
Suddenly, just beyond it, they heard footsteps descending a flight of stairs. Slow footsteps, thudding solemnly-approaching the door! Then came the rattle of a chain.
''Quick!'' gasped Frank. ''Get back into the tunnel!"
The boys scrambled swiftly through the rock doorway, and swung it shut after them. But they did not close it entirely. They heard the other wooden door creak open slowly. The Hardys, peeping through the narrow slit they had left, saw Asa Grable standing on the threshold!
CHAPTEE XXIII
THE SMELL OF DANGER
Ready to slam the door shut and hold it against capture, the Hardy boys watched Asa Grable.
The elderly scientist was revealed plainly in the glare of an electric light hanging from the ceiling at the foot of the stairs. He was muttering to himself. Under one arm he carried a large square glass jar full of earth.
Instead of proceeding farther, he set the jar carefully on the floor and turned back. Evidently this was a closet he used for special experiments. He did not close the door behind him. The boys saw him putter around for a moment in the room beyond. Then he ascended the stairs. His echoing footsteps became fainter and fainter, then died away.
The brothers glanced at each other. Should they follow Asa Grable? Perhaps he had merely gone back for something he had forgotten. Frank decided that they should watch the man's movements. There was too much at stake not to do so. In a moment the boys had closed the rock doorway and were across the threshold of the other one. Silently they proceeded up the steep flight of stairs.
Light fell through a half-open doorway at the top of the steps. There, crouching in the shadows, Frank and Joe peered into the room beyond.
It was Asa Grable's secret laboratory, where Joe had witnessed the synthetic rubber experiment. In the glow of light from a solitary desk lamp they saw the elderly scientist examining a solution in a test tube. Then, quite unaware of the eager eyes watching him, he turned away from the table and went over to a cupboard. He unlocked the door. When he turned around, he was carrying over one arm a long black robe.
The Hardy boys were stunned!
They could scarcely believe what they saw. Joe's discovery of the torch handles in Grable's laboratory had been damaging enough. Their coming upon the secret tunnel that led directly to the scientist's laboratory had been equally suspicious. But they were not prepared for this final clue, with all its implications that Asa Grable was actually one of the hooded men.
"Mr. Grable!" called a familiar voice.
The scientist looked up. ''I'm coming, Archibald,'' he answered. ''I'm coming right away.''
Down the stairs from the office came Archibald Jenkins. He was carrying a torch handle. The younger man seemed flustered and anxious.
"I called to you a few minutes ago but you didn't answer," he said, handing Asa Grable the torch handle.
"Guess I didn't hear you, Archibald," returned the scientist mildly. "I'll come along right away."
Archibald Jenkins returned up the stairs again. The elderly scientist followed. The Hardy boys could hear the murmur of their voices, but they could not distinguish what the two men were saying. A door swung shut at the head of the stairs.
Frank and Joe darted into the secret laboratory. Lightly they sped up the steps, until they reached the closed door at the head of the flight. They were just in time to hear Archibald Jenkins say:
"All right then, I'll tell them two o'clock. Is that satisfactory?"
"Two o'clock sharp," answered Asa Grable.
"Fine. In the meantime, you'd better get some sleep. It will be a hard ordeal for you."
"Yes, I suppose I should go to bed and get a little rest," the scientist agreed. "Turn out the light, Archibald. Be sure to lock all the doors before you leave."
"Don't worry. I'll see that everything is locked up tight. Good night."
"Good night, Archibald."
The Hardys heard a door open and close. They could see a crack of light beneath the door of the office. Archibald Jenkins was moving about alone. Finally the light was extinguished and the man's footsteps receded. The boys were by no means certain that Jenkins had left the building. He might have gone into another office.
"I think we've learned all we're going to learn here,'' whispered Frank. ''And we might be caught getting out of here, if the burglar alarm should go off. Let's go back into the mine."
"Suits me." Joe turned and made his way quietly down the stairs. "I wouldn't want to run into Archibald Jenkins at this stage of the game. He might think we know too much."
The boys returned to the secret laboratory but they did not linger there. They went oil down the second flight of stairs, through the doorway into the tiny passage, and through the rock doorway. Frank glanced at his watch.
"Ten o'clock," he said quietly. "We still have time to do some more exploring here, if nothing big is going to happen until two o'clock."
"You could have sold me out for a nickel when I saw Grable take that black robe out of the closet," Joe declared. "To think of him being one of the hooded men!"
"Of course we could be wrong."
"That robe settles it so far as I'm concerned. And what's going on at two o'clock? Do you think there's to be a meeting of the flickering torch outfit?"
"It might be." Frank was puzzled. "This ought to clear up the mystery for us, but it doesn't. It only makes everything more puzzling than ever. Is Grable robbing his own greenhouses?''
"That's what I keep asking myself. Maybe his greenhouses haven't been robbed at all. Perhaps that's just a blind, so that if we notice anything suspicious going on around here, it can be blamed on burglars.''
There seemed to be no satisfactory explanation. From the beginning the Hardy boys had trusted Asa Grable, had seen no reason to doubt his word about the robberies. And yet the black robe and the torches were so incriminating that they seemed to offer only one answer.
In silence the boys made their way back down the long, narrow tunnel. Suddenly Joe sniffed.
"Notice that odor?"
They could detect a faint, pungent scent in the tunnel. As they proceeded, it became stronger.
"Must be a skunk loose in the mine," chuckled Joe. "Whew! That's mighty powerful. I hope we don't run into him."
He advanced a few more paces. But Frank came to a sudden stop.
"Joe! Come back!" he said sharply.
His brother turned. "What's the matter? You aren't afraid of a nice little black and white skunk, are you?"
Frank grabbed Joe's arm, hurriedly pulled him back along the tunnel. "That odor means danger," he snapped urgently. "We must get out of here. And quickly!''
He hustled Joe back along the tunnel. Then he broke into a run. His brother was completely mystified.
"I don't get this," he panted, hurrying along. "Skunks aren't dangerous."
"That skunk smell is synthetic. It's a new system they have of warning miners of danger. With noisy drills the men can't hear alarm bells. And with an individual light to work by, they might not notice the main ones being turned off and on."
"So they blow a skunk odor in. And nobody would miss that! Great Scott! Why didn't I think of that!'' Joe scrambled madly down the passage. "I wonder what they're warning the men about."
Even as he spoke, they heard a dull thud somewhere back of them. Blasting! If Frank had not realized the significance of the artificial odor, they might have run right into death. Even now they were not clear of the deadly peril. Another explosion might come at any moment, tumbling rocks and earth upon them.
"Quick!" gasped Frank.
They raced back toward the door that would lead them to safety. The tunnel narrowed. Their flashlights shone on the two rocks that shielded the hidden door. Frank pulled on them. They swung out, and the hinges creaked dismally. Anxiously the boys rushed into the tiny passage beyond. In another moment they would be in the safety of the underground laboratory.
They had closed the laboratory door behind them when they had left. But they had not been able to lock it for the padlock was on the inside. Frank thrust himself against the door.
"If we can only get out of Grable's office without being seen–"
Then he uttered a cry of alarm. The door did not respond to his thrust. Frank pushed on it again. The barrier was rigid and unyielding.
"Jenkins must have locked it since we left!"
Gasping for breath, perspiration streaming down their faces, the Hardy boys leaned against the locked entrance. But they could not budge it.
"What'll we do?" cried Joe.
Frank tried to think. In a moment he became less excited. "I believe the blasting is over. We'll go back and get out the other way."
As they went through the tunnel again, it seemed different. The skunk odor was less pronounced, but the slight draft the boys had felt before was gone.
"Something is the matter!" said Joe.
He soon learned what it was. The blasting evidently had taken place near the entrance to the tunnel which led to Grable's laboratory. Now that opening was completely blocked! And the air was choked with dirt and smoke.
"Frank! We're trapped!" Joe cried, hurrying back out of the smoke and dust-filled area.
Frank followed. "Everybody has gone out of the mines," he said grimly. "And Grable and Jenkins have locked all their doors and gone. Nobody knows we're here, so there'll be no search."
"My head is swimming now." Joe coughed.
"I feel dizzy myself," said Frank. "Oh, Joe, we mustn't go to sleep!"
"Do you suppose some poison gas was released by the blast?" Joe was gasping now.
"I'v ufr»v2 so," replied Frank groggily.
CHAPTER XXIV
THE HIDE-OUT
"We must get through, that door!" gasped Frank. "It's our only chance!"
He thrust his shoulder against the barrier. The door shook. The ancient hinges creaked. But it did not yield.
Joe stumbled forward. ''The rock!''
Together the boys picked up the top stone of the ones piled against the outer doorway, and heaved it. The barrier to Grable's place seemed to give a little. Encouraged, the boys drew back, flinging the stone again and again. There was a sharp snap, followed by a clatter of broken metal.
"Once again!" gasped Frank.
This time the door crashed heavily inward. The impact had shattered the old padlock. The boys rushed into the inner room and slammed the door shut behind them. Even in that musty chamber the air seemed fresh by comparison with the air in the tunnel they had just left. They sat down a few minutes until they felt better.
"Our robes and torch handles!" said Frank, dismayed.
''They 're just outside,'' replied Joe, recalling that they had laid them down there the first time they had tried the door.
Quickly he retrieved them. Then, grasping the hooded gowns and torches, he and Frank scrambled up the stairs to Grable's secret laboratory. They went on up the next flight into the office above.
All the lights were out. Frank tried the office door. It was locked. Joe peered outside. The place seemed to be deserted.
"The coast is clear. Shall we make a run for it?"
"I think we ought to go right over to Wortman's and find out what's doing there."
Frank pulled open the door. Instantly the raucous clang of the burglar alarm resounded noisily, raising brassy echoes from every part of the property. The Hardy boys sprang through the doorway, slammed the door behind them, and ran. They were not five yards from the office before they saw lights flashing in the Grable cottage and heard shouts.
Frank led the way, heading straight for the open fields. Once in the darkness there they felt safe from pursuit, but they ran until they were sure no one from the Grable place could see them. When they looked back, they noticed lights flashing here and there. Apparently the burglar alarm had aroused the whole establishment.
"I wish we could find Dad," panted Frank. "There's so much to tell him."
They stopped at the Trumper farmhouse to inquire for a message. The woman told them their father had telephoned, saying he and Mr. Cartwright were on their way to Wortman's cottage.
"Maybe he's there now," said Joe excitedly. "Come on, Frank."
As the boys made their way through the meadow, which they had to cross on their way to the Wortman place, it was strange to think of the mine workings lying far beneath them. Apparently the villagers did not suspect that the long-forgotten tunnels were in use again. Wortman and his gang had been clever in covering up their tracks, so that neither the mine operations nor the hiding of the stolen goods had aroused a hint of suspicion in the neighborhood.
''To think that we 've been living right across the way from that place and never realized what was going on!" whispered Joe, as they climbed the fence and reached the mysterious cottage.
The place was in darkness and seemed deserted. Then they saw a flash of light. It gleamed once. Then there was a pause and two quick flashes.
"A signal of some kind," Frank said quietly. "We'd better sneak up carefully or we're likely to run into another trap."
Frank's caution was well-founded. They kept to the shelter of the low bushes along the fence, and halted just before they reached the yard. As they did so, they heard a door open. A man stepped out of the cottage.
A moment later a shadowy figure emerged from a clump of trees near the end of the lane. He was followed by another.
"That you, Jim?" said the man in front of the cottage door.
The Hardy boys recognized his voice. Hal Wortman!
"Yes, Charlie is with me," returned the hooded figure.
"Good," said Wortman. "I was hoping you'd see the signal."
"Anything gone wrong?" asked the second hooded figure.
''Plenty,'' growled Wortman. ''Come inside and get your robes. I have an errand for you.''
He opened the door. The three went into the cottage.
The moment the door closed, the Hardy boys crept forward. They were sure they had not been observed. But hardly had they emerged from the shelter of the hedge than two figures rose quietly out of the darkness and sprang upon them. Frank felt a heavy jolt as he was thrown to the ground. His impulsive cry was stifled by a hand clapped over his mouth.
"Well," muttered a familiar voice, "I've got one of them!"
It was the voice of Fenton Hardy!
"And I have the other," hissed Detective Cartwright. "Let's have a look at them."
The boys were hauled to their feet. Frank had a wild impulse to roar with laughter when he saw his father's face peering at him in the gloom. But he knew enough not to do so.
"Why, it's–I thought you had left," exclaimed Fenton Hardy in astonishment. He released his son and turned to Cartwright. "Let them go!" he whispered.
In low tones Frank told of the brothers' recent findings. He held up the robe and the torch handle, telling of Grable's mention of two o'clock.
"Something is going to happen sooner," said his father. "Get into that robe–quickly," he snapped. "Do each of you have one? Good! Now get back here in the shadows, and when those men come out again, do what I tell you. I collected a lot of damaging evidence this afternoon.''
Hastily the Hardy boys scrambled into the robes, drew the hoods down over their heads. Frank thought he understood his father's plan. The boys hardly had disguised themselves before the cottage door opened. Wortman and two men came out, carrying their hooded cloaks.
"Now remember," their leader was saying, "the rest of the men aren't to come here tonight under any circumstances. It's your job to go to the cliff and warn them."
"Where's the truck?" asked the one who had been addressed as Jim a few minutes earlier.
"It's hidden by the lilac hedge on old lady Trumper's property. Now remember, when you go to the cliff, give the signal with the torches as I've told you. That will warn the others to stay away. But don't wave the torches from side to side, because they'll take that as a signal to come on."
"We need some kerosene on these rags," said the other man, removing the cloth-wrapped rod from the handle.
''Give them to me. There's a drum of kerosene at the back of the house. And put those robes on. I want to be sure you 're goin' to wear 'em right."
Wortman disappeared around the corner of the house with them. Jim and Charlie stood waiting in the yard. Before they had a chance to put on the black cloaks, the Hardy boys saw their father and Cartwright steal out from the darkness of the hedge. They moved swiftly but noiselessly, almost invisible in the gloom. They stole up behind the unsuspecting figures.
One of the men turned suddenly. But in the same instant Fenton Hardy and Cartwright sprang. The others were overpowered and silenced with gags before they could utter a cry. The two detectives dragged the struggling prisoners back into the darkness of the hedge. At the same time Fenton Hardy whispered urgently to his sons:
''You boys take their places! I'll keep watch here until you bring the others. There are more of the flickering torch gang in Wortman's cellar!"
Grasping the torch handles, Frank and Joe sprang from the hedge and hurried toward the front of the cottage. In the long robes, their faces hidden by the hoods, they could not be distinguished from the pair who had been there a moment before.
They were just in time. Hal Wortman emerged from behind the building.
"Here you are," he said, and thrust the kerosene-soaked rags into the torch handles. "You look all right. Take off those robes now and be on your way. And come back here when you've warned off the others."
Silently, Joe and Frank turned and walked off. But they had gone scarcely ten feet before Wortman called out:
"Here! Wait a minute!"
Apparently his suspicions had been aroused when the boys had failed to take off the cloaks.
"Something queer about this," he muttered. "You aren't–"
He never finished, because Fenton Hardy leaped swiftly from the hedge. Wortman went down, bowled over by the sudden impact of the detective's rush. He uttered a gurgling cry.
Frank and Joe hurried off. They removed the cumbersome robes, and raced down the path across the field to Mrs. Trumper's place.
The truck was where Wortman had said it would be, hidden by the lilac hedge. They jumped into it. Frank took the driver's seat. The engine roared. He swung the wheel, and the vehicle shot out into the lane. It bounced wildly along the rutted road until it reached the highway. It swerved out onto the concrete.
"I hope Dad and Cartwright can capture that crew,'' said Joe. ''Maybe we'll be lucky enough to round up all the rest of them."
Frank swung the truck down the road past Grable's. Where was that man now? The machine sped toward the new road project. The Hardy boys were trembling with excitement. In five brief minutes the tables had been turned. Wortman and two of his aides