“Sorry, Tony, I didn’t mean that. Tell me about the collar.”

“Well, that’s all. There was no collar in the bag last night. Shirt, socks, tie⁠—everything except a collar. Why?”

“Was that what you were looking for in the cupboard?” said Bill eagerly.

“Of course. ‘Why no collar?’ I said. For some reason Cayley considered it necessary to hide all Mark’s clothes; not just the suit, but everything which he was wearing, or supposed to be wearing, at the time of the murder. But he hadn’t hidden the collar. Why? Had he left it out by mistake? So I looked in the cupboard. It wasn’t there. Had he left it out on purpose? If so, why⁠—and where was it? Naturally I began to say to myself, ‘Where have I seen a collar lately? A collar all by itself?’ And I remembered⁠—what, Bill?”

Bill frowned heavily to himself, and shook his head.