Meanwhile, another part of the strange mystery was being enacted with the girls as princ.i.p.al characters. They had entered farther into the secret pa.s.sage, beyond the queer swinging door which had closed after them.

"We're caught!" cried Belle. "Oh, Cora!"

"Perhaps not," said Jack's sister. "If that door opened once for us it will do it again. But don't go back. Come on. We must see what is ahead of us. The boys will laugh if they hear we turned back when we had such a good opportunity."

"Well, they shan't laugh at _me_!" declared Hazel. "I'm with you, Cora."

"And you may be sure we're not going to be left alone," cried Bess.

"Come on, Belle!"

The latter hesitated a moment, looked back at the closed door, and then went forward. Their lamps made the place fairly light, and they could see that the pa.s.sage was planked here as it had been nearer the bungalow.

They had gone on perhaps fifty paces more and were wondering when the queer tunnel would come to an end, when Cora, who was walking in advance with Hazel, put her hand on her companion's arm, and cried:

"Do you hear it?"

"Hear what?"

"That strange, rumbling, trembling noise. Don't you _feel_ it?"

"Yes! Yes!" cried Belle. "Oh, what is it?"

There was no doubt of the noise. It seemed to fill the whole pa.s.sage with a dull, rumbling roar, and the ground vibrated and trembled.

"Come on!" cried Cora, resolutely. "It's just ahead of us. We will solve the mystery now!"

Willing or unwilling, Belle, Bess and Hazel followed their leader. With their electric lights showing the way the girls pressed forward.

Suddenly the pa.s.sage turned, and, making that turn, the girls came upon a strange sight.

Before them was an open door, which gave entrance to a large cave with rocky sides and roof. Vaulted and large the cave was, and from long wires fastened somewhere in the roof hung a number of incandescent lights. In the cave the girls saw several queer machines, and Cora, at least, recognized more than one of them as printing presses. A gasoline engine was throbbing away in one corner, and it was this, Cora decided, which made the rumbling, the throbbing and trembling vibrations.

Hardly realizing what they were doing, the girls walked forward, and, pa.s.sing through the open door, entered the cave which widened out at the end of the secret pa.s.sage.

"What-what does it all mean?" asked Bess.

Low as her voice was it seemed to awaken strange echoes in the vaulted cave. And at the sound of it something stirred in one corner. From a pile of boxes something arose-a something that resolved itself into an old man with white hair and a long, white beard. He peered from beneath his bushy white eyebrows, with piercing eyes at the startled girls, and from his throat came a guttural cry.

"Ah, ha! Police spies-four of 'em!" he snarled. "I thought we'd be found out!"

With surprising quickness in one seemingly so aged the man slipped behind the girls. They turned, fearing an attack, but they need have had no alarm on that score. With a quick motion the old man closed and locked the door through which they had come.

"Now you're here-you'll stay!" he rasped out. "On guard here, Bombee!

Hist! Watch 'em!"

And, as he called, a raw-boned, half-witted boy shuffled forward, and squatted, with a horrible grin, in front of the terrified girl prisoners.

CHAPTER XXIX-TO THE RESCUE

Jack and his two chums, waiting in the dark of the cave, wondered who it was approaching. They had guessed it would prove to be the two men who had gone down the road shortly before in Cora's car, but this was only a guess. And whether these two were the same men who had first taken the machine was, of course, only a conjecture.

"What'll we do, Jack?" whispered Paul, from behind a barrel where he was crouching. "Jump out on 'em?"

"No," was the answer. "Not at first. Let's see what their game is and then we'll have better evidence against them. Just lie low and wait."

"Here they come!" cautioned Walter.

The sound of the footsteps and of the voices was nearer now, and presently the boys saw the glimmering reflection of light on the rocky and dirt sides of the cave.

"We've got to work lively!" said a man's voice. "Those campers are beginning to suspect there's something wrong. We'll have to clear out, bag and baggage, presses, engine and everything."

"That's right," added another. "Lucky we have the car. We can take most of the stuff in that if we have time, and set it up somewhere else. This graft is too good to give up."

"Where'll we take it?" a third voice asked, and the boys, who could not see the speakers, wondered how many of them there were.

"Oh, we can stow it away at--" began the man who had spoken first when there came an interruption from his companion.

"No names!" he cautioned.

"Who's to hear?"

"You can't tell. Since those boys opened up the floor of the bungalow, there's no telling what might have happened. Besides, I don't want old Jason to know where we are going. I'm going to get rid of him; he's more trouble than help."

"Especially with that horrible boy of his," some one said. "Ugh! I can't bear the creature!"

"Still he's been useful. He did the tricks all right. But it was a mistake to go to the bungalow. That's caused all the trouble. We should have stuck to this end of the cave."

"We had to have an emergency exit," declared one of the men, "and the bungalow was the best."

"Yes, until these campers came. Now that jig is up."

"Yes, the whole business is up, I'm afraid. Well, let's see what we can get out now before we're found."

Jack and his chums could hear the men moving about boxes and barrels.

They seemed to be taking them outside. What was in the packages the boys could only guess. And Jack was wondering what he and his companions could do if the men in the cave should suddenly discover the presence of the intruders.

Jack peered out from behind his barrel and had a glimpse of a man moving about in the light of a lantern the criminals had brought into the cave with them. But the man's legs alone were visible and Jack could form very little idea from them of how the man looked.

"Isn't this enough for one load?" asked one of the men. "We don't want a breakdown."

"Oh, that machine will carry more," declared another. "We did a fine stroke when we picked that up. I wonder if those girls have an idea where their car went to?"

"They'll have one soon," thought Jack, gritting his teeth. "The nerve of you!"

"Let's go back and get that little numbering press," suggested a man.