Tom Swift was up at break of day, and the others were not far behind him.

"Now for the secret cave!" cried the young inventor as he gazed up the mountain, in the interior of which the mysterious band of men were making the diamonds.

"Have you made any plans, Bill?" asked Mr. Jenks of the former phantom, who had cast his lot in with the adventurers. "What will be the best course for us to follow?"

"You just leave it to me, Mr. Jenks," was the answer. "I'll get you into the cave, and those fellows, who, I believe, are trying to do me out of my rights, as they did you out of yours, will never know a thing about it."

"Bless my finger-nails!" cried Mr. Damon. "That will be great!" We can get in the cave, and watch them make the diamonds at our leisure."

"They don't make them every day," explained Renshaw. "It seems they have to wait for certain occasions. Mostly they make the diamonds when there's a big storm."

"A big storm" asked the scientist with a sudden show of interest. "Do you mean one of those electrical storms, such as we had the other night?"

"That's it, Mr. Parker, though why they wait until there's a storm is more than I can tell."

"Perhaps they know that on such occasions no one will venture up the mountain," spoke Mr. Damon.

"No, it isn't that," declared the scientist. "I think I am on the track of a great scientific discovery, and I will soon be able to make observations that will confirm it."

"Well, I'm going to make an observation right now," said Tom, with a laugh. "I'm going to see what there is for breakfast."

"And that reminds me," came from Mr. Jenks, "shall we move our camp, Bill, and take the tent with us to the cave?"

"I hardly think so," was the answer. "I think the best plan would be to conceal the tent somewhere around here, in case you might need it again. You can also store what food you have left."

"But, bless my appetite, we don't want to starve in that diamond cave!" objected Mr. Damon.

"I'll see that you don't," declared Bill Renshaw. "I'll take you in there, unbeknownst to those fellows, and I'll provide you with plenty of food and water. You see the cave is so big that there are some parts they never visit."

"And we can stay in one of those parts, and eat?" asked Tom.

"Sure," answered Bill.

"And watch the diamond makers at work?" asked Mr. Jenks.

"That's it," replied the former phantom.

"Then the sooner we get started the better," remarked Mr. Damon. Mr. Parker said nothing. He appeared to be thinking deeply, and was tapping at some rocks with his little hammer.

The advice of Bill Renshaw was followed, and the tent, and what food remained, was concealed in the bushes, with rocks piled over to keep away prowling animals. Then they started for the secret cave.

The man who played the part of a ghost picked up the framework and white cloth that had formed his disguise.

"I'll still have to use this," he explained, "for I don't want those fellows to know that I'm helping you. I'll continue to play the spirit of the mountain, but there won't be much need of it. I don't think any more people will come prospecting out here."

"Have you heard of the arrival of Farley Munson?" asked Tom, as he related the facts about the stowaway.

"He hadn't arrived up to a day or so ago," answered Bill. "I guess he's still traveling. Farley is one of the heads of the gang," he added, "and a dangerous man."

As Bill led the way toward the cave, taking a route that the adventurers had never suspected led to it, he explained that the cavern was a large one, capable of holding an army.

"But there's only a small part of it used by the diamond makers," he added. "They work in a small recess, near the summit of the mountain. The little cave, where I'm going to take you, opens off from it by a long passage. And, except that you'll be pretty much in the dark, you'll be quite comfortable. There are tables, chairs, and some bunks in the place. I can get you some lights, and plenty of food."

"But, if you are seen taking away food, won't the others suspect something?" asked Tom.

"I do pretty much as I please," said Bill. "I go and come when I like. All I'm supposed to do is to watch my two sides of the mountain, play the ghost, and give warning when any one is coming. Sometimes I leave black and white messages, like the one I put on your tent. Those fellows fix 'em up for me. I've told 'em about you, though I didn't know who you were, and they think you have gone, for the two men on guard at the rear entrance so reported. Sometimes I stay out on the mountain for a couple of days at a time, when the weather's good, and don't go back to the cave. Those times I take food with me, and so if they see me making off with some supplies they'll think I'm going to camp out."

"It doesn't look as though we'd ever get into a cave near the top of the mountain, going this way," said Tom, as they marched along. "We're going down, instead of up."

"That's the secret of this trail," explained Bill. "We go down in a sort of valley, and then go up a pretty stiff place, and then we're on a direct trail to the entrance I told you about. It's a steep road to climb, but I guess we can manage it."

And a hard climb the adventurers did find it. The road was almost as bad as the one along the edge of the chasm, but they managed to negotiate it, and finally found themselves on a fairly good trail.

"We'll soon be there," Bill assured them. "After you get in the little cave, where I'm going to hide you, I'll have to leave you for a spell, until I get my ghost rigging fixed up again. But I'll see that you have plenty of food and drink."

A little later their guide came to a sudden halt, and peered around anxiously.

"What's the matter?" asked Tom.

"I was just looking to see if any of the men were about," he answered. "But I guess not--it looks all right. The entrance is right here."

They were on a side of the mountain, near the summit. Below stretched a magnificent scene. A great valley lay at their feet, and they could look off to many distant peaks. The main trail to Leadville, and the one to the settlement of Indian Ridge, was in sight.

Suddenly Tom, who had been using a small but powerful telescope, uttered an exclamation, and focussed the instrument on a speck that seemed moving along on the trail below.

"A man--coming up the mountain," cried Tom. "And--it can't be-- yet it is--it's Farley Munson--the stowaway!" he cried. "He's coming here!"

"Let me look!" begged Mr. Jenks, taking the glass from Tom. An instant later the diamond man exclaimed: "Yes, it's Munson!"

"Then in here with you--quick!" cried Renshaw. "He can't see us yet, and we'll be out of sight in another minute."

The former spirit pulled aside some thick bushes, and pointed to a hole which was disclosed.

"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.