He had boarded the car alone and without thought of plunder. Had it been in professional hours, he would have had at least one "stall"--perhaps two--with him. As chance would have it, a portly business man, with a massive gold chain spanning his ample waist, had seated himself next the operator. And Fred had decided that the watch on the end of the cable was worth risking an experiment upon. Besides, the appearance of prosperity of the "mug" spoke of a possible "leather" stuffed with banknotes. Decidedly, even in the absence of a "stall," it was worth chancing. And then Foyle got on and spoilt it all. If any one on the tramcar lost anything he would know who to blame. For Heldon Foyle had spoiled one of the greatest coups that ever a crook had been on the verge of bringing off. Fred, immaculately clad, and with irreproachable references, had approached Greenfields, the Bond Street jewellers, with a formula for manufacturing gold. He had discovered the philosopher's stone. "Of course, I don't want you to go into this until I've proved that it can actually be done," he said airily. "See there. I made that handful of gold-dust myself. You test it, and see that it's all right. Now, I'll sell you the secret of making that for £100,000. I don't want the money till I've given you a demonstration." So an arrangement was fixed up. The jewellers, with a faith that long experience had not destroyed, believed in Fred. Nevertheless, they took the precaution of calling in Foyle, then unknown to Fred save by name. In a little room in Clerkenwell the experiment took place. With ingenious candour, Fred prepared a crucible in front of his select audience after the various ingredients had been submitted to strict examination. Then he placed it on the fire, and stirred the contents occasionally. At last the process was finished, and at the bottom of the crucible was found a teaspoonful of undoubted gold-dust. Then, while Fred, with a broad smile of satisfaction, awaited comment, the detective, who had noted the strange fact that he had kept his gloves on while stirring the crucible, stepped up to him and deftly whipped one off. In the fingers were traces of gold-dust--enough to convict Fred and get him three years at the Old Bailey. Out of the corner of his eyes, Fred watched the detective presently stand up and pass along the deck of the car towards him. The operator's face was bland, and he smiled with the consciousness of one who has nothing to hide as the superintendent sat down beside him. "Hello, Mr. Foyle! I am glad to see you," he said, with a heartiness that he knew did not deceive the other. "It's a long time since we met." The detective returned the greeting with a cheerfulness that was entirely unassumed. "It's a piece of luck meeting you, Freddy," he went on. "But there, I always was lucky. You're just the man in the wide world I've been wanting to see." "What's on?" growled Freddy, with quick suspicion.