"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 I'' 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 Ms father and the other detective tried to open the door to the building.

171 "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 ishef"

"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 miud, that it was entirely a personal animosity of Boots toward the boys.

172 "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 ch.o.r.es 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 pa.s.sed it a num173 her 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 hole 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 is any bottom," said Frank. He poised himself for a dive, and 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 174 this neighborhood. If there's any story connected with this pool, she's bound to know it."

There was was a story connected with the pool. As Frank had guessed, the Widow Trumper 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 a.s.sured 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 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.

175 "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 I"

CHAPTER XXI.

UNDERGROUND.

job 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.

176.

177 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 178 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 pa.s.sage 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 pa.s.sageway 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!

179 The footsteps echoed loudly in the pa.s.sageway. 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 lootl" he whispered hoa.r.s.ely.

180 The tunnel was so long they could not see tht 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 "Is he or he or isn't isn't he one of them?" 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 pa.s.sageway. In the glow of the electric lights they saw a man trudging straight toward them. He was about fifty yards away, and under hia 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.