For a moment he felt a sinking sensation. To be chained fast in the dark, at the bottom of some cave or dungeon, located he knew not where, was enough to take the heart out of any one. But not for long did Tom Swift give way to despair. He gave a vigorous tug to the chain about his ankle. After all, it might only be lying across it or loosely twisted. But it needed only one effort on his part to loosen the links to let him know that he was bound fast. Whoever had put the chain on his ankle had done so with serious intentions of holding the young inventor captive. “Well, this is worse and more of it!” he mused grimly. “What does it all mean? It can’t be a plot to kidnap me. No one knew I was coming across the lots, for I didn’t know it myself until the last minute. And seeing that man sneaking along, discovering the secret stairs—it was all a series of accidents. Though it’s likely to prove a serious accident for me if I can’t get loose.” Tom was nothing if not practical, and first he felt about with his hands to determine the exact nature of what it was that held him fast. He discovered, by the sense of touch, that something in the nature of a handcuff was snapped about his ankle. To this cuff, or leg-iron, was attached a chain. By following this, link by link, Tom found that the chain was made fast to a ring of iron which, in turn, was sunk into the stone side wall of the cave or tunnel in which he now found himself. How far he was removed from the bottom of the flight of secret steps where he had been made unconscious, he did not know, any more than he knew where he was. Having discovered what it was that held him fast and the nature of the chain and its fastenings, Tom, who had risen to his feet, stood silent a moment, listening. It was very black and very still in the cave, if such it was, and from the earthy, damp smell he concluded that he must be underground, or at least in some vault or cellar. By test Tom found that he could move about five feet, such being the length of the chain. The leg-iron had been snapped or riveted about his ankle outside of his trousers. It was not tight enough to cause any pain, but it was snug enough to be impossible of removal. “They’ve got me as tight as an animal in a trap!” grimly exclaimed the youth, when, by a series of tugs, he ascertained how securely the end of the chain was fast in the rocky wall. “Just like a trap, or a prisoner in an old-time dungeon!” bitterly reflected the young man. “All it needs to make a moving picture film is some beautiful maiden to come to my rescue with a file——” Tom’s spoken words (for he was talking aloud to himself) came to a sudden end as he clapped a hand to the pocket of his coat. “I’ve got ’em!” he fairly shouted, and he drew out a small paper parcel in which were two keen files. They were part of the purchases made just before stumbling on the mysterious man and finding the steps in the queer opening.