"Do you think there is any danger of them finding us?" asked Mr. Damon, as he hurried along beside Tom.

"I'm afraid so," was the answer. "I've been worried ever since we saw Munson heading this way. But we couldn't do any differently."

"Perhaps Bill Renshaw may be able to conceal us," suggested Mr. Jenks. "Very likely he knows that Munson is on hand. Perhaps we will be safe for a while. I want to make a few more observations as to how they manufacture the diamonds, and then, with what I already know, I'll have the secret."

"And I'd like to make some scientific tests of the sides and bottom rocks of the cave," spoke Mr. Parker. "I think it will bear out my theory that the mountain will soon be destroyed."

"Well, you were right about Earthquake Island, and you may be right about this mountain," said Tom, "but if it is going to be annihilated I hope we get far enough away from it."

We can keep our presence here a secret for a few more days, I think that will be long enough," proceeded Mr. Jenks. "Then we will leave."

"And, in the meanwhile, they'll be searching for us," objected Mr. Damon. "I wish that ghost-chap would come back and tell us what to do. Bless my liver-pin, but we are going to be in considerable danger, I'm afraid! Those men may capture us, and decide to make diamond dust from us."

"Come on--hurry to the little cave," urged Tom. "Then we'll get ready to defend ourselves."

"The main cave is a large one," said Mr. Jenks, "and there are many hiding places in it. In fact, it is so large that it will take those fellows several days to complete a circuit of it. By that time Bill Renshaw may come back, and take us to some place in which they have already searched for us. Then we'll be comparatively safe."

This thought was some consolation to them, as they made their way through the dark passage, dimly illuminated by the lantern they had rekindled, to the place where Bill had hidden them. They found things as they had left them, and proceeded to get a meal, though Tom said it would be best not to cook anything, or even to make coffee, for fear the odors would enable the searchers to trail them.

So they ate cold food, glad to get that. Silently they sat about the dimly-lighted cavern, and discussed the situation. True they might even now retreat, going out of the entrance Bill had showed them, and so escape. But Mr. Jenks felt that his mission was not completed yet, and they all agreed to stay with him.

"For there are several points about making diamonds that are not quite clear to me," he said. "I need to know how that steel box is constructed, how the electrical switches are arranged, what kind of lightning rods they use, and how they regulate the pressure. The other things, and how to mix the ingredients, I already know."

"Then we'll do our best to help you," promised Tom. "But now I think we had better see what sort of a defense we can put up. We have our guns and revolvers, and with these chairs and tables we can build a sort of barricade behind which we can take refuge if those fellows do discover our hiding place."

This was conceded to be a good idea, and soon a rude sort of fort was made, behind which the adventurers could take their stand and fight, if necessary, though they hoped this would not come to pass.

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.