was distinctly interested.

"That's rather hot," he said. "Expound."

"Well, I can't explain it, whether it's something in the actual eye, or
something in the brain, or what, but I have got rather an uncanny habit
of recording things unconsciously. You know that game where you look at
a tray full of small objects for three minutes, and then turn away and
try to make a list of them. It means a devil of a lot of concentration
for the ordinary person, if he wants to get his list complete, but in
some odd way I manage to do it without concentration at all. I mean that
my eyes seem to do it without the brain consciously taking any part. I
could look at the tray, for instance, and talk to you about golf at the
same time, and still get my list right."

"I should think that's rather a useful gift for an amateur detective.
You ought to have gone into the profession before."

"Well, it is rather useful. It's rather surprising, you know, to a
stranger. Let's surprise Cayley with it, shall we?"

"How?"

"Well, let's ask him--" Antony stopped and looked at Bill comically,
"let's ask him what he's going to do with the key of the office."

For a moment Bill did not understand.

"Key of the office?" he said vaguely. "You don't mean--Tony! What do you
mean? Good God! do you mean that Cayley--But what about Mark?"

"I don't know where Mark is--that's another thing I want to know--but
I'm quite certain that he hasn't got the key of the office with him.
Because Cayley's got it."

"Are you sure?"

"Quite."

Bill looked at him wonderingly.

"I say," he said, almost pleadingly, "don't tell me that you can see
into people's pockets and all that sort of thing as well."

Antony laughed and denied it cheerfully.

"Then how do you know?"

"You're the perfect Watson, Bill. You take to it quite naturally.
Properly speaking, I oughtn't to explain till the last chapter, but I
always think that that's so unfair. So here goes. Of course, I don't
really know that he's got it, but I do know that he had it. I know that
when I came on him this afternoon, he had just locked the door and put
the key in his pocket."

"You mean you saw him at the time, but that you've only just remembered
it--reconstructed it in the way you were explaining just now?"

"No. I didn't see him. But I did see something. I saw the key of the
billiard-room."

"Where?

"Outside the billiard-room door."

"Outside? But it was inside when we looked just now."