"Should we by any chance manage to secure the fellow, I will let you know," said Reiffenburg, as we stood together at the front door. "I fear, however, _we shall not be so fortunate_." There was a sneer in his voice, for which I could have kicked him. However, I kept my temper, and murmuring something to the effect that I was glad to have been of service, I took my departure, and the door closed behind me. "That was one of the most extraordinary affairs I have ever known," I said to the detective, as we turned our faces homewards. "I am quite at a loss to account for it." The detective stopped suddenly and looked at me. "The lady and gentleman are particular friends of yours, sir, I understand, and I don't know in that case whether I ought to tell you what is in my mind. But I fancy I could throw a rather unexpected light upon the affair." "Speak out, then, by all means," I answered. "What was it you noticed?" "This, sir," he said, and as he spoke he took from his pocket a small piece of black matter about half the size of a pea. He handed it to me and asked if I had seen it before. I informed him that I was quite sure I had not. "It only bears out, sir, what I was saying as we came down Park Lane, just before we reached Wiltshire House. If it weren't for little things, that they overlook, we shouldn't be able to lay our hands on half the criminals we want. Now mind you, sir, I don't mean to infer by that that your friend Count Reiffenburg is a criminal. Not at all; that would be a very wrong thing to say. He's probably been playing a practical joke, as gentlemen will. The fact, however, remains that he gave himself away with that little lump of black stuff, just as surely as Bill Coakes of the Minories did when he gave his sweetheart the silk handkerchief that he picked up in old Mrs Burgiss's bedroom. He didn't think it was of any importance, but she wore it, quarrelled with a girl over it, the police came to hear of it, and Bill was caught. So it was just that slip that brought him to the gallows." "I do not understand you," I replied, still holding the tiny bit of black stuff in my hand. "What is the connection between this substance and Count Reiffenburg?" "It's the key to the whole puzzle, sir," he said, and took it from me. Turning his face away, he put his hand to his mouth, and then wheeling round again, parted his lips and showed me his teeth. The eye-tooth on the right-hand side was missing. He put up his hand once more, and lo! it was restored to its place. "That's what I mean, sir," he said. "Now I noticed, when the gentleman came downstairs, that one of his eye-teeth were missing. He wanted to make himself look old, I suppose, and when he had taken off the other pieces, had forgotten to remove that one. Then he must have remembered it, for his hand went up to his mouth, and next minute it was on the floor, where I managed to get hold of it."