To face the fellow boldly and unflinchingly was, I recognised, the only way in which to gain the knowledge I sought. Yet in the garb of a mechanic, was I not much handicapped? Nevertheless, I walked back, and, finding the hall porter, gave my name as Flynn, and asked to see Mr. Seymour upon important business. After a wait of nearly ten minutes a man in uniform came and ushered me up in the lift to the third floor, where, having traversed a long, thickly-carpeted corridor, he opened a door and allowed me to pass across the small well-furnished hall of the flat into a sitting-room, where I found myself again face to face with my mysterious neighbour. He started at sight of me, but so perfect an actor was he that in a second he had recovered himself, and inquired with affected friendliness: "Why, my dear Holford, why in the name of Fate did you send up your name as Flynn?" "Because I wished to see you, Mr. Kirk," was my hard response, for we were now alone together in that cosy, sumptuously-furnished sitting-room, through the windows of which I could see the dark flowing Thames and the row of gleaming lights on the Surrey shore beyond. "I knew," I added, "that if I had sent up my own name I should not be received." "Why?" he asked, opening his eyes widely. "I don't follow you. Surely you have acted as a good friend to me, therefore why shouldn't I receive you? I've only this very moment returned from abroad. Who told you I was back again?" "No one. I obtained the knowledge for myself," I said, "and I have come here, Mr. Kirk, for several reasons, the chief being to ask you a simple and pointed question: who killed Professor Greer?" "My dear sir," he exclaimed, looking straight at me with unwavering gaze, a slight change, however, showing in his thin, grey countenance, "that is the very problem that I myself am trying to solve--but in vain." "An impostor is passing himself off as Greer," I declared. "Is he?" asked Kirk quietly. "I was not aware of that." "Not aware of it!" I cried in angry dismay. "Do you actually deny, then, that you are acquainted with this man who has taken the personality and honours of Professor Greer upon himself in order to preserve the secret of the unfortunate scientist's death?" "I deny being aware of any person attempting to pass himself off as Greer," was my mysterious neighbour's bold and unflinching reply. Had I not sent that telegram from Broadstairs and signed it Kirk, and had not its receipt caused the false Professor quickly to change his quarters? Kirk's reply staggered me. "Look here," I exclaimed again, raising my voice in anger at this open denial of what I knew to be the truth, "on the night of your escape from Sussex Place, the house was searched, and I found evidences of all traces of the crime having been effaced in the furnace of the laboratory."