"Well, Mr. Jenks," began Tom, when he had descended to the garden, and greeted the man who had acted so strangely on Earthquake Island, "this is rather an odd time for a visit."

"I realize that, Tom Swift," was the answer, and the lad noticed that the man spoke much more calmly than he had that evening at the jewelry shop. "I realize that, but I have to be cautious in my movements."

"Why?"

"Because there are enemies on my track. If they thought I was seeking aid to discover the secret of Phantom Mountain, my life might pay the forfeit."

"Are you in earnest, Mr. Jenks?"

"I certainly am, and, while I must apologize for awakening you at this unseemly hour, and for the mysterious nature of my visit, if you will let me tell my story, you will see the need of secrecy."

"Oh, I don't mind being awakened," answered Tom, good- naturedly, "but I will be frank with you, Mr. Jenks. I hardly can believe what you have stated to me several times--that you know how diamonds can be made."

"I can prove it to you," was the quiet answer.

"Yes, I know. For centuries men have tried to discover the secret of transmuting base metals into gold, and how to make diamonds by chemical means. But they have all been failures."

"All except this process--the process used at Phantom Mountain," insisted the queer man. "Do you want to hear my story?"

"I have no objections."

"Then let me warn you," went on Mr. Jenks, "that if you do hear it, you will be so fascinated by it that I am sure you will want to cast your lot in with mine, and aid me to get my rights, and solve the mystery. And I also want to warn you that if you do, there is a certain amount of danger connected with it."

"I'm used to danger," answered Tom, quietly. "Let me hear your story. But first explain how you came to come here, and why you acted so strangely at the jewelry store."

"Willingly. I tried to attract your attention at the store, because I saw that you were going to buy a diamond, and I didn't want you to."

"Why not?"

"Because I want to present you with a beautiful stone, that will answer your purpose as well or better, than any one you could buy. That will prove my story better than any amount of words or argument. But I could not attract your attention without also attracting that of the jeweler. He became suspicious, gave chase, and I thought it best to vanish. I hope no one was made to suffer for what may have been my imprudence."

"No, the lad whom Mr. Track caught was let go. But how did you happen to come to Shopton?"

"To see you. I got your address from the owner of the yacht Resolute. I knew that if there was one person who could aid me to recover my rights, it would be you, Tom Swift. Will you help me? Will you come with me to discover the secret of Phantom Mountain? If we go, it will have to be in an airship, for in no other way, I think, can we come upon the place, as it is closely guarded. Will you come? I will pay you well."

"Perhaps I had better hear your story," said the young inventor. "But first let me suggest that we move farther away from the house. My father, or Mr. Jackson, or the housekeeper, may hear us talking, and it may disturb them. Come with me to my private shop," and Tom led the way to a small building where he did experimental work. He unlocked the door with a key he carried, turned on the lights, which were run by a storage battery, and motioned Mr. Jenks to a seat.

"Now I'll hear your story," said Tom.

"I'll make it as short as possible," went on the queer man. "To begin with, it is now several years ago since a poorly dressed stranger applied to me one night for money enough to get a meal and a bed to sleep in. I was living in New York City at the time, and this was midnight, as I was returning home from my club.

"I was touched by the man's appearance, and gave him some money. He asked for my card, saying he would repay me some day. I gave it to him, little thinking I would hear from the man again. But I did. He called at my apartments about a week later, saying he had secured work as an expert setter of diamonds, and wanted to repay me. I did not want to take his money, but the fact that such a sorry looking specimen of manhood as he had been when I aided him, was an expert handler of gems interested me. I talked with the man, and he made a curious statement.

"This man, who gave his name as Enos Folwell, said he knew a place where diamonds could be made, partly in a scientific manner, and partly by the forces of nature. I laughed at him, but he told me so many details that I began to believe him. He said he and some other friends of his, who were diamond cutters, had a plant in the midst of the Rocky Mountains, where they had succeeded in making several small, but very perfect diamonds. They had come to the end of their rope, though, so to speak, because they could not afford to buy the materials needed. Folwell said that he and his companions had temporarily separated, had left the mountain where they made diamonds, and agreed to meet there later when they had more money with which to purchase materials. They had all agreed to go out into civilization, and work for enough funds to enable them to go on with their diamond making.

"I hardly knew whether to believe the man or not, but he offered proof. He had several small, but very perfect diamonds with him, and he gave them to me, to have tested in any way I desired.

"I promised to look into the matter, and, as I was quite wealthy, as, in fact I am now, and if I found that the stones he gave me were real, I said I might invest some money in the plant."

"Were the diamonds good?" asked Tom, who was beginning to be interested.

"They were--stones of the first water, though small. An expert gem merchant, to whom I took them, said he had never seen any diamonds like them, and he wanted to know where I got them. Of course I did not tell him.

"To make a long story short, I saw Folwell again, told him to communicate with his companions, and to tell them that I would agree to supply the cash needed, if I could share in the diamond making. To this they agreed, and, after some weeks spent in preparation, a party of us set out for Phantom Mountain."

"Phantom Mountain?" interrupted Tom. "Where is it?"

"I don't know, exactly--it's somewhere in the Rockies, but the exact location is a mystery. That is why I need your help. You will soon understand the reason. Well, as I said, myself, Folwell and the others, who were not exactly prepossessing sort of men, started west. When we got to a small town, called Indian Ridge, near Leadville, Colorado, the men insisted that I must now proceed in secret, and consent to be blindfolded, as they were not yet ready to reveal the secret of the place where they made the diamonds.

"I did not want to agree to this, but they insisted, and I gave in, foolishly perhaps. At any rate I was blindfolded one night, placed in a wagon, and we drove off into the mountains. After traveling for some distance I was led, still blindfolded, up a steep trail.

"When the bandage was taken off my eyes I saw that I was in a large cave. The men were with me, and they apologized for the necessity that caused them to blindfold me. They said they were ready to proceed with the making of diamonds, but I must promise not to seek to discover the secret until they gave me permission, nor was I to attempt to leave the cave. I had to agree.

"Next they demanded that I give them a large sum, which I had promised when they showed me, conclusively, that they could make diamonds. I refused to do this until I had seen some of the precious stones, and they agreed that this was fair, but said I would have to wait a few days.

"Well, I waited, and, all that while, I was virtually a prisoner in the cave. All I could learn was that it was in the midst of a great range, near the top, and that one of the peaks was called Phantom Mountain. Why, I did not learn until later.

"At last one night, during a terrific thunder storm, the leader of the diamond makers--Folwell--announced that I could now see the stones made. The men had been preparing their chemicals for some days previous. I was taken into a small chamber of the cave, and there saw quite a complicated apparatus. Part of it was a great steel box, with a lever on it.

"We will let you make some diamonds for yourself," Folwell said to me, and he directed me to pull the lever of the box, at a certain signal. The signal came, just as a terrific crash of thunder shook the very mountain inside of which we were. The box of steel got red-hot, and when it cooled off it was opened, and was given a handful of white stones."

"Were they diamonds?" asked Tom, eagerly.

Mr. Jenks held out one hand. In the palm glittered a large stone--ostensibly a diamond. In the rays of the moon it showed all the colors of the rainbow--a beautiful gem. "That is one of the stones I made--or rather that I supposed I had made," went on Mr. Jenks. "It is one of several I have, but they have not all been cut and polished as has this one.

"Naturally I was much impressed by what I saw, and, after I had made certain tests which convinced me that the stones in the steel box were diamonds, I paid over the money as I had promised. That was my undoing."

"How?"

"As soon as the men got the cash, they had no further use for me. The next I remember is eating a rude meal, while we discussed the future of making diamonds. I knew nothing more until I found myself back in the small hotel at Indian Ridge, whence I had gone some time previous, with the men, to the cave in the mountain."

"What happened?" asked Tom, much surprised by the unexpected outcome of the affair. "I had been tricked, that was all! As soon as the men had my money they had no further use for me. They did not want me to learn the secret of their diamond making, and they drugged me, carried me away from the cave, and left me in the hotel."

"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!"