“But why not have kept them in the passage?”

“He was frightened of the passage.  Miss Norris knew about it.”

“Well, then, in his own bedroom, or even, in Mark’s.  For all you or I or anybody knew, Mark might have had two brown suits.  He probably had, I should think.”

“Probably.  But I doubt if that would reassure Cayley.  The brown suit hid a secret, and therefore the brown suit had to be hidden.  We all know that in theory the safest hiding-place is the most obvious, but in practice very few people have the nerve to risk it.”

Bill looked rather disappointed.

“Then we just come back to where we were,” he complained.  “Mark killed his brother, and Cayley helped him to escape through the passage; either in order to compromise him, or because there was no other way out of it.  And he helped him by telling a lie about his brown suit.”

Antony smiled at him in genuine amusement.

“Bad luck, Bill,” he said sympathetically.  “There’s only one murder, after all.  I’m awfully sorry about it.  It was my fault for—­”

“Shut up, you ass.  You know I didn’t mean that.”

“Well, you seemed awfully disappointed.”

Bill said nothing for a little, and then with a sudden laugh confessed.

“It was so exciting yesterday,” he said apologetically, “and we seemed to be just getting there, and discovering the most wonderful things, and now—­”

“And now?”

“Well, it’s so much more ordinary.”

Antony gave a shout of laughter.

“Ordinary!” he cried.  “Ordinary!  Well, I’m dashed!  Ordinary!  If only one thing would happen in an ordinary way, we might do something, but everything is ridiculous.”  Bill brightened up again.

“Ridiculous?  How?”

“Every way.  Take those ridiculous clothes we found last night.  You can explain the brown suit, but why the under clothes.  You can explain the underclothes in some absurd way, if you like—­you can say that Mark always changed his underclothes whenever he interviewed anybody from Australia—­but why, in that case, my dear Watson, why didn’t he change his collar?”

“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?”