“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.”