“Didn’t you try to find the cave again?”

“I did, but without avail.  I spent some time in the Rockies, but no one could tell where Phantom Mountain was; in fact, few had heard of it, and I was nearly lost searching for it.

“I came back East, determined to get even.  I had given the men a very large sum of money, and, in exchange, they had given me several diamonds.  Probably the stones are worth nearly as much as the money I invested, but I was cheated, for I was promised an equal share in the profits.  These were denied me, and I was tricked.  I determined to be revenged, or at least to discover the secret of making diamonds.  It is my right.”

“I agree with you,” spoke Tom.

“But, up to the time I met you on Earthquake Island, I could form no plan for discovering Phantom Mountain, and learning the secret of the diamond makers,” went on Mr. Jenks.  “I carried the gems about with me, as you doubtless saw when we were on the island.  But I knew I needed an airship in which to fly over the mountains, and pick out the location of the cave where the diamonds are made.”

“But how can you locate it, if you were blindfolded when you were taken there, Mr. Jenks?”

“I forgot to tell you that, on our journey into the mountains, and just before I was carried into the cave, I managed to raise one corner of the bandage.  I caught a glimpse of a very peculiarly shaped cliff—­it is like a great head, standing out in bold relief against the moonlight, when I saw it.  That head of rock is near the cave.  It may be the landmark by which we can locate Phantom Mountain.”

“Perhaps,” admitted the young inventor.

“What I want to know is this,” went on Mr. Jenks.  “Will you go with me on this quest—­go in your airship to discover the secret of the diamond makers?  If you will, I will share with you whatever diamonds we can discover, or make; besides paying all expenses.  Will you go, Tom Swift?”

The young inventor did not know what to answer.  How far was Mr. Jenks to be trusted?  Were the stones he had real diamonds?  Was his story, fantastical as it sounded—­true?  Would it be safe for Tom to go?

The lad asked himself these questions.  Mr. Jenks saw his hesitation.

“Here,” said the strange man, “I will prove what I say.  Take this diamond.  I intended it for you, anyhow, for what you did for me on Earthquake Island.  Take it, and—­and give it to the person for whom you were about to purchase a diamond to-night.  But, first of all, take it to a gem expert, and get his opinion.  That will prove the truth of what I say, Tom Swift, and I feel sure that you will cast your lot in with mine, and help me to discover the secret of Phantom Mountain, and aid me to get my rights from the diamond makers!”

CHAPTER IV—­ANDY FOGER GETS A FRIGHT

Tom Swift considered a few minutes.  On the face of it, the proposition appealed to him.  He had been home some time now after his adventures on Earthquake Island, and he was beginning to long for more excitement.  The search for the mysterious mountain, and the cave of the diamond makers, might offer a new field for him.  But there came to him a certain distrust of Mr. Jenks.