“Why do you keep from me the fact that you were in the bank the night before last when this horrible tragedy occurred?” He did not answer immediately. “I have not kept it from you,” he said. “I have practically admitted it--in an unguarded moment, I confess, but I did admit it.” “What were you doing there?” she demanded. “Making my fortune,” he said solemnly. But she was not to be put off by his flippancy. “What were you doing there?” she asked again. “I was watching three interesting burglars at work,” he said, “as I have watched them not once but many times. You see, I am specially gifted in one respect. Nature intended me to be a burglar, but education and breed and a certain lawfulness of character prohibited that course. I am a dilettante: I do not commit crime, but I am monstrously interested in it. I seek,” he said slowly, “to discover what fascination crime has over the normal mind; also I have an especial reason for checking the amount these men collect.” Her puzzled frown hurt him; he did not want to bother her, but she knew so much now that he must tell her more. He had thought it would have been possible to have hidden everything from her, but people cannot live together in the same house and be interested in one another’s comings and goings without some of their cherished secrets being revealed. “What I cannot understand----” she said slowly and was at a loss for an introduction to this delicate subject. “What cannot you understand?” he asked. “I cannot understand why you suddenly dropped all your normal pleasures, why you left the Foreign Office, why you gave up music, and why, above all things, that this change in your life should have come about immediately after the playing of the ‘Melody in F.’” He was silent for a moment, and when he spoke his voice was low and troubled. “You are not exactly right,” he said. “I had begun my observations into the ways of the criminal before that tune was played.” He paused. “I admit that I had some fear in my mind that sooner or later the ‘Melody in F’ would be played under my window, and I was making a half-hearted preparation against the evil day. That is all I can tell you,” he said. “Tell me this,” she asked as he rose, “if I had loved you, and had been all that you desired, would you have adopted this course?” He thought awhile. “I cannot tell you,” he said at length; “possibly I should, perhaps I should not. Yes,” he said, nodding his head, “I should have done what I am doing now, only it would have been harder to do if you had loved me. As it is----” he shrugged his shoulders. He went out soon after, and she found the paper he had been reading, and without difficulty discovered the advertisement. Then he was the Hatton Garden intruder, and what he had said was true. He had observed these people, and they had known they were being observed.