“The entrance to the secret cave,” he announced.  “Slip in all of you.”

Tom, after another glance at the man toiling his way up the mountain, entered the cavern.  He was followed by the others.  Bill was the last to enter, and he replaced the bushes over the entrance.

“At last!” exclaimed Mr. Jenks, as he gazed up at the roof of the dimly-lighted vault in which they found themselves.

“Yes, we’re in the diamond makers’ secret cave,” added Tom.  “Now to catch them at work!”

“Come on,” advised Bill, in a low tone, “We’re not safe yet,” and he produced a lantern from some hidden recess, lighted the wick, and led the way.  As the others followed they were aware of a subdued noise in the great cavern.

CHAPTER XX—­MAKING THE DIAMONDS

“What’s that noise?” asked Tom, as their guide flashed the lantern to show them the way.

“That’s the men getting ready to make diamonds, I guess,” was the answer.  “You see it takes quite a while to get the stuff ready.  I don’t know what they use—­they never tell me any of their secrets.”

“Oh, I know the ingredients well enough,” said Mr. Jenks, “but I don’t know the secret of how they apply the terrific heat and pressure necessary to fuse the materials into diamonds.”

“Well, you’ll soon know,” declared Bill Renshaw.  “Of course it isn’t always successful.  I’ve known ’em to try half a dozen times before they got any diamonds big enough to satisfy ’em.  They gave me some of the small ones when I asked for my wages.

“How did you come to get in with these men?” asked Tom, curious to understand how a person seemingly as honest as Renshaw appeared to be had cast his lot in with the men who had broken faith with Mr. Jenks.

“Oh, I’ve lived around these parts all my life,” was the answer.  “I knew of this cave before these diamond fellers came to it.  In fact, I showed it to ’em.  It was several years ago that a party of men who were prospecting around here came to me and asked if I knew of a small cave near the top of a high mountain, where lightning storms were frequent.  I told them about Phantom Mountain, as it was called then, and also of this cave.  If there’s any place where they have worse lightning storms than here, I’d like to know it.  They scare me, sometimes, like the night when that landslide happened, and I’m sort of used to ’em.

“Well, I took these men to the cave, and they hired me as a sort of lookout.  Then they began their work, and at first I didn’t know what they were up to, but finally I caught on.  Then Mr. Jenks came, and disappeared mysteriously, though then I didn’t know that they had played a trick on him.  I was outside most of the time, pretending I was the ghost.  So that’s how I came to get in with ’em, and I wish I was out.”

“You soon will be, I think,” declared Mr. Jenks.  “But won’t our talking be heard by the men?”