In Indian file we mounted to the first floor, to find ourselves in a second, identical room, also stripped of furniture and decorations. Harley barely glanced out of the northern window, shook his head, and: “Next floor, Pedro,” he directed. Up we went, our footsteps arousing a cloud of dust from the uncarpeted stairs, and the sound of our movements echoing in hollow fashion around the deserted rooms. Gaining the next floor, Harley, unable any longer to conceal his excitement, ran to the north window, looked out, and: “Gentlemen,” he said, “my experiment is complete!” He turned, his back to the window, and faced us in the dusk of the room. “Assuming the ash stick to represent the upright body of Colonel Menendez,” he continued, “and the sheet of cardboard to represent his head, the hole which I have cut in it corresponds fairly nearly to the position of his forehead. Further assuming the bullet to have illustrated Euclid’s definition of a straight line, such a line, _followed back_ from the yew tree to the spot where the rifle rested, would pass through the hole in the cardboard! In other words, there is only one place from which it is possible to see the flame of the candle _through the hole in the cardboard_: the place where the rifle rested! Stand here in the left-hand angle of the window and stoop down! Will you come first, Knox?” I stepped across the room, bent down, and stared out of the window, across the Tudor garden. Plainly I could see the sun-dial with the ash stick planted before it. I could see the piece of cardboard which surmounted it--and, through the hole cut in the cardboard, I could see the feeble flame of the candle nailed to the ninth yew tree! I stood upright, knowing that I had grown pale, and conscious of a moist sensation upon my forehead. “Merciful God!” I said in a hollow voice. “It was from _this window_ that the shot was fired which killed him!” CHAPTER XXXIV THE CREEPING SICKNESS From the ensuing consultation in the library we did not rise until close upon midnight. To the turbid intelligence of Inspector Aylesbury the fact by this time had penetrated that Colin Camber was innocent, that he was the victim of a frame-up, and that Colonel Juan Menendez had been shot from a window of his own house. By a process of lucid reasoning which must have convinced a junior schoolboy, Paul Harley, there in the big library, with its garish bookcases and its Moorish ornaments, had eliminated every member of the household from the list of suspects. His concluding words, I remember, were as follows: “Of the known occupants of Cray’s Folly on the night of the tragedy we now find ourselves reduced to four, any one of whom, from the point of view of an impartial critic uninfluenced by personal character, question, or motive, or any consideration other than that of physical possibility, might have shot Colonel Menendez. They are, firstly: Myself.