They remained quietly in the cave the remainder of that day, and, when it was night, as they could tell by their timepieces—­there was no daylight—­they divided the hours into watches, taking turns standing guard.

Morning, at least in point of time, came without any disturbance, and they made a cold breakfast.  They hoped that Bill Renshaw would come, but he did not appear.

After sitting in the dark cave until afternoon, Tom said: 

“I think we might as well go and take another observation of the big cave.  We can tell what the men are doing, then, for they don’t seem to have been near us.  Maybe they have given up the search for us, and we can see them at work, and Mr. Jenks can gain what further knowledge he needs.”

“That will be a good plan,” agreed the diamond man.  “It’s maddening to sit here, doing nothing.”

“And it will be comparatively safe to go from here to our former post of observation,” added Tom, “for there doesn’t seem to be any opening along the tunnel, into the larger cave, except the place where we were.”

Accordingly they started off.  Cautiously they looked through the opening into the apartment where they had seen the diamonds made.

“There’s not a soul here!” exclaimed Tom, in a whisper.  The others looked.  The place was deserted—­the machinery silent.  Mr. Jenks peered in for a moment, and then exclaimed: 

“I’m going in!  Now’s my chance to find out all that I wish to know!  It may never come again, and then we can soon leave Phantom Mountain!”

It was a daring plan, but it seemed to be the best one to follow.  They were all tired of inactivity.  Mr. Jenks managed to get through the opening, and dropped into the big cave.  The others followed.  Mr. Jenks hurried over to the steel box, and began an examination of it.  Tom Swift was looking at the electrical switch.  He saw how it was constructed.  Mr. Damon and Mr. Parker were peering interestedly about.

Suddenly the sound of voices was heard, and the echo of footsteps.  Mr. Jenks started.

“They’re coming back!” he whispered hoarsely.  “Run!”

They all turned and sped toward their hiding place.  But they were too late.  An instant later Folwell, Munson and the other diamond makers confronted them.  Our friends made a bold rush, but were caught before they could go ten feet.

“We have them!” cried Munson.  “They walked right into our hands!”

It was true.  Tom Swift and the others were the prisoners of the diamond makers.

CHAPTER XXIII—­BROKEN BONDS

“Well,” remarked Tom Swift, in mournful tones, “this looks as if we were up against it; doesn’t it?”

“Bless my umbrella, it certainly does,” agreed Mr. Damon.

“And it’s all my fault,” said Mr. Jenks.  “I shouldn’t have gone into the big cave.  I might have known those men would come back any time.”