"His collar?" said Bill in amazement.

"His collar, Watson."

"I don't understand."

"And it's all so ordinary," scoffed Antony.

"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.

"Don't ask me, Tony. I can't--By Jove!" He threw up his head,
"In the basket in the office bedroom!"