Bob pushed him back gently. "He's safe, too."

Frank sank back, relieved. "What happened?" he said, after a while.

"We saw the smoke when you and Joe started up the slope," Bob told him, "and figured you were going to investigate it."

166.

167 "When the smoke disappeared and you didn't return," d.i.c.k added, "we came up on the ridge to find you."

Bob nodded. "Then we saw the open crevice and crawled in. Smoke started to come up and we were about to climb out when we saw your light. That's all," he concluded simply.

It was far from all, Frank knew. It must have Saken plenty of courage and strength for Bob and d.i.c.k to rescue the boys from the smoke-filled tunnel at the risk of their own lives.

His lips smiled at the two engineers, but his eyes spoke his grat.i.tude.

Joe stirred on the ground beside him, and Bob and d.i.c.k gave their attention to the other Hardy boy. Frank looked about him. A short distance away, smoke still was pouring in a tall column from the open fissure.

Some time later when they had returned to camp, Frank and Joe told the engineers in detail what had happened. Somewhere deep inside the mountain, they were convinced, was the scene of the Klenger gang's activities. When they described the gurgling stream at the base of the crevice, Bob and d.i.c.k stared.

"Do you think it was flowing from the valley?'8 Bob asked excitedly.

"That's my hunch," Frank told him.

The boys told the engineer of their plan to descend the crevice the next day. If they found the 168 water was not flowing, they could all be certain then that the tunnel at the base of the crevice ran from the reservoir and carried the water which Bayport so desperately needed.

"d.i.c.k and I will join you," Bob said promptly. "But first, we'll equip ourselves with gas masks," he added significantly, "or our next trip down the crevice may be our last!"

"There are some gas masks in your office in Bay-port," d.i.c.k told him. "I stowed 'em there after our last field trip. Guess I'd better go get them."

"Let us get them!" Frank and Joe said in unison -then broke off, laughing.

Joe explained that it was important that the boys' father be told about the cavern they believed was concealed in the mountain, so he could take steps to a.s.sure the capture of Klenger's gang.

Bob agreed, and gave the youths the key to his office.

"You'll find the gas masks in the closet," d.i.c.k told lihem.

Once again, the Hardy boys found themselves on the highway between Skull Mountain and Bayport. They had arranged to meet the engineers at the crevice on top of Skull Mountain early in the morning.

Frank drove rapidly, and the cool night air rushing into the speeding roadster cleared away every sensation the boys retained of their desperate adventure in the smoky tunnel.

169 They stopped at Bob's office to pick up the gas masks, then drove through the streets of Bay-port. The usually bustling business section seemed strangely quiet and deserted, until the boys remembered it was almost midnight.

As they approached Klenger's shop, Frank slowed the car and the boys looked carefully through the plate-gla.s.s window. Then, swiftly, the elder Hardy boy brought the roadster to a stop a few feet beyond the store.

In the rear of the shop they had seen a light!

The boys walked stealthily back to the window and peered in through the gla.s.s. The glare came from a transom over the door of Klenger's office.

Joe tried the door of the shop. It was unlocked. He started to open it, but Frank motioned to him to wait.

"Hold it," he whispered.

Frank looked along the deserted street. In front of a fruit store, a few doors away, some empty crates had been piled at the curb to be picked up by the rubbish collectors.

He carried a crate to the door and stood it on its end. Then he stood on the crate and pushed open the door a few inches with one hand, while with the other he stuffed a portion of his handkerchief between the bell which announced a customer's entry into the shop and its hammer.

"It can't give us away now," he whispered to Joe with a grin, and pushed the door wide.

170 They slipped into the shop, closing the door quietly behind them.

The door to Klenger's office was closed, but the rransom was slightly ajar, and the boys could hear a faint murmur of voices.

Joe gestured to Frank, and they tiptoed toward fche office. As they came to the end of the counter, they heard a m.u.f.fled thumping.

"What was that?" Joe whispered, startled.

The thumping sounded again.

The boys leaned over the counter and looked down. Someone was lying on the floor of the store *-bound and gagged!

Joe ran around the counter and struck a match. A pair of eyes looked at him appealingly, and a voice made strangled noises behind the gag.

It was Chet Morton!

CHAPTER XX.

Mrs. Klenger Intervenes.

joe removed the gag from Chet Morton's mouth and loosened the short pieces of wire which bound his hands and feet.

"Wow!" Chet gasped. "Am I glad you two came along!"

"Not so loud," Frank cautioned him in a low voice, glancing toward the office.

"How did it happen?" Joe asked.

In an undertone Chet recounted how, after a late movie, he had walked through the neighborhood toward the lot where his car was parked and decided to pa.s.s by the plumbing shop to see if everything was in order.

To his surprise, he saw a light-and cautiously investigated. But a bell tinkled the moment Chet stepped into the shop, and he barely had time to bat an eye before he found himself bound and gagged and dumped behind the counter.

171.

172 "I guess I'm not much of a detective," Chet sighed dejectedly as the boys grinned. He looked at them queerly. "Hey," he inquired. "How come the bell didn't ring when you you came came in?"

Joe described Frank's use of the handkerchief.

"What I don't understand," the blond-haired boy whispered, frowning, "is why the men didn't lock ;he door after they discovered you were able to enter the shop."

"Lock's jammed," Chet replied promptly. "I heard one of the men say so."

"Who were the men, Chet?" Frank queried.

"Sweeper and Limpy," he told Frank. "They went into that office at the back of the store."

The three boys looked at the light in the transom over the closed door. Although they could hear the men's voices, the sound was too faint for them to distinguish the words.

Suddenly a new sound came through the slightly open transom-a sustained, rushing noise similar to the sound the boys used to make by blowing across the rim of a drinking gla.s.s.

The youths stared at one another, puzzled. Frank tiptoed close to the door and placed a chair beside it. He mounted the chair and gently pushed open the transom a few inches more. Then he looked inside the office.

Sweeper and the man with the limp were kneeling on the floor in front of a small iron safe. Sweeper 173 was holding an acetylene torch, and its bluish flame was cutting a circle through the metal around the lock of the safe.

Frank felt a tug at his trouser leg and looked down. It was Chet. Joe had discovered the door's keyhole was empty, and was intently observing the men through the tiny aperture. But Chet was completely mystified as to what was taking place.

He looked up at Frank, his face tortured with curiosity. "What's going on?" he demanded in a hoa.r.s.e whisper.

Frank started to tell his impatient friend, then wisely decided to climb down from the chair lest his voice carry through the transom.

"They're cracking the safe with a blowtorch," he told Chet when he was standing beside him.

"Blowtorch!" the boy breathed. "Lemme see!"

He climbed eagerly up on the chair.

"Take it easy, Chet," Frank whispered urgently, "or you'll give us away!"

Chet nodded rea.s.suringly, then tried to peek through the transom. But being inches shorter than Frank, he found his eyes were below the tilted gla.s.s.

"I can't see!" he whispered. "Try to locate a couple of books for me to stand on, w.i.l.l.ya?"

Frank sighed and nodded reluctantly. Something told him Chet was headed for trouble.

He brought back a few bound catalogues from the counter and stacked them on the seat of the chair.

174 Chet climbed on top of the stack, teetering precariously.

"Watch out-!" Frank whispered sharply.

He sprang forward to support the youth, but Chet was past all aid. He gave Frank a wild, despairing look as the catalogues skidded out from under him, and he had to leap to the floor past the tumbling books!

The boys heard startled exclamations from inside the office-and the acetylene torch was shut off.

"Behind the counter!" Frank whispered. "Quick!"

He pulled the chair from its position in front of the door, and then the three youths ducked behind the end of the long counter loaded with plumbing gadgets.

A moment later, the office door was flung open, and Sweeper stared out.

Limpy's face, pale with fright, appeared at the Hhin man's shoulder.

"What was it?" he asked, trembling.

Sweeper stared at the books sprawled near the upright chair. At that moment a black cat walked into the rectangle of light which streamed through the open doorway. He stopped and looked at the two men, then meowed piteously.

Sweeper laughed.

"A snooping cat-that's what it was!" he said, pointing. "Must've jumped on the chair and knocked all those books off!"

175 He picked up a book and threw it at the animal. The cat squealed with fright and anger, and ran to another part of the shop.

"Black!" Limpy whispered, staring after it. "That means bad luck!"

"Forget it," Sweeper told him shortly. He went back into the office. "Come on," he said impatiently. "We've got to finish this job."

The small man limped after him and closed the door.

Soon, the boys heard the sound of the acetylene torch again. They crept out from behind the counter, and Frank again placed the chair beside the door.

"This time," he whispered to Chet, "you stay on the floor where nothing can happen-I hope!"

He stood on the chair and peered through the transom, while Joe resumed his position at the keyhole.

Sweeper and Limpy were concentrating on the safe, but their voices could be heard over the sound of the blowtorch.

"Plane all set for the getaway?" Sweeper asked.

Limpy nodded. "It's waiting for us at the south end of the airport."

Getaway! Airport!

Frank signaled a huddle.

"We've got to think of some way to stop them," he muttered to the others. "But how?"

176 "We'd better ask Dad to take a hand in this," Joe whispered. "Those men may have guns."

Frank approved, but Chet shook his head.

"Won't work," he whispered back. "Your dad's in Washington."

"Washington!" gasped Joe.