"I was thinkin' about something to do with John Bohun's attempt to kill Lord Canifest, when he didn't succeed but thought he had…"
In the gloom beside him, Bennett felt the girl stiffen. She stared up at him uncomprehendingly; but he gestured her fiercely to be silent. They were eavesdroppers, but he was afraid to speak up-afraid to move now. He regretted coming down here, when something in Katharine's restless brain seemed impelling her to talk. He pressed her arm.
"But we'll skip all that for a minute," continued H. M. drowsily, "and look at this impossible situation. The first thing is to determine the murderer's motive. I don't mean his motive for murder, but for creating an impossible situation. That's very important, son, because it's the best kind of clue to the motive for murder. Why'd he do it? Nobody but a loony is goin' to indulge in a lot of unreasonable hocus-pocus just to have some fun with the police. And there are enough motives for Tait's murder flyin' about already without our needin' to explain the mess by simply saying that the murderer is crazy. Well, then, what reasons could there have been?"
"First, there's the motive of a fake suicide. That's fair enough. I go to your house, shoot you through the head, and shove the gun into your hand. Say it's a house like this one, with little panes in the windows. Uh-huh. I lock and bolt the door of the room on the inside. I've got with me a bag containing a piece of glass cut just right, I've got tools and putty. I remove one of the panes of glass in the window nearest the catch. Then I climb out the window, reach through, and lock it on the inside. Afterwards I replace the old pane with my new little one; I putty it round, smear it with dust so nothing shows, and walk away. And so the room's all locked up, and they'll think you shot yourself."
Masters peered at him uncertainly.
"It strikes me, sir," he said, "that you know every dodge-"
"Sure I know every dodge," H. M. grunted sourly. He stared at the fire. "I've seen so many things, son, that I don't like to think of 'em at Christmas. I'd like to be home at my place drinkin' hot punch and trimmin' a Christmas tree. But let's sorta poke and prod at this thing. If it's a new wrinkle in the art of homicide, I want to know all about it. First, the suicidefake is barred. Nobody tries to stage a fake suicide by beatin' a woman's head.
"Second, there's the ghost-fake, where somebody tries to make it look like a supernatural killing. That happens seldom; it's a tricky business at best, and. entails a long careful build-up of atmosphere and circumstances. And obviously that's out of the question in this murder too, since nobody's ever tried to foist any suggestion of the kind or so much as intimated that the pavilion's haunted by a murderous spook.
"Finally, there's accident. There's the murderer who creates an impossible situation in spite of himself, without wantin' to. Say you and Inspector Potter are sleepin' in connectin' rooms, and the only outside door, which is to his room, is barred on the inside. I want to kill you and throw suspicion on him. I come in during the night, workin' my pane-and-putty trick on the window; I stab you in the dark, and get out after replacin' the pane. Yes. What I forget or don't observe is that the door connecting your room with his is also locked on your side — and I've got an impossible situation again. Ayagh!
"Now that's the last and final refuge. But burn me," said H. M., suddenly turning round the glare of his small eyes, "can you see how that last and final refuge can be applied to this mess? Accident, hey? What kind of accident is it where a person DON'T make tracks in the snow?"