I had to remind myself that he was talking about definitions of similarity and difference, and not about me personally.

“What about the open window, when all the windows in the other two rooms are closed?” he asked. “Is that a difference worth noting?”

“It’s unlikely to be relevant,” I said. “Richard Negus might have opened the window himself. There would be no reason for the murderer to close it. You’ve said it often yourself, Poirot—we Englishmen open windows in the dead of winter because we believe it’s good for our character.”

“Mon ami,” said Poirot patiently. “Consider: these three people did not drink poison, fall out of their armchairs and quite naturally land flat on their backs with their arms at their sides and their feet pointing toward the door. It is impossible. Why would one not stagger across the room? Why would one not fall out of the chair on the other side? The killer, he arranged the bodies so that each one was in the same position, at an equal distance from the chair and from the little table. Eh bien, if he cares so much to arrange his three murder scenes to look exactly the same, why does he not wish to close the window that, yes, perhaps Mr. Richard Negus has opened—but why does the murderer not close it in order to make it conform with the appearance of the windows in the other two rooms?”

I had to think about this. Poirot was right: the bodies had been laid out in this way deliberately. The killer must have wanted them all to look the same.

Laying out the dead . . .

“I suppose it depends where you choose to draw your frame around the scene of the crime,” I said hurriedly, as my mind tried to drag me back to my childhood’s darkest room. “Depends whether you want to extend it as far as the window.”

“Frame?”

“Yes. Not a real frame, a theoretical one. Perhaps our murderer’s frame for his creations was no larger than a square like this.” I walked around Richard Negus’s body, turning corners when necessary. “You see? I’ve just walked a small frame around Negus, and the window is outside the frame.”

Poirot was smiling and trying to hide it beneath his mustache. “A theoretical frame around the murder. Yes, I see. Where does the scene of a crime begin and where does it end? This is the question. Can it be smaller than the room that contains it? This is a fascinating matter for the philosophers.”

“Thank you.”

“Pas du tout. Catchpool, will you please tell me what you believe happened here at the Bloxham Hotel yesterday evening? Let us leave motive to one side for the moment. Tell me what you think the killer did. First, and next, and next, and so on.”

“I have no idea.”

“Try to have an idea, Catchpool.”