cunning piece of mechanism. The table I examined was

a duplicate, perfectly innocent. It was substituted for

the other immediately after the murder. The thing was

worked from the flat below, which, if you remember,

was let furnished. But one accomplice at least was in

Savaronoff's flat. The girl is an agent of the Big Four, working to inherit Savaronoff's money."

"And Ivan?"

"I strongly suspect that Ivan is none other than the famous Number Four."

"What?"

"Yes. The man is a marvellous character actor. He

can assume any part he pleases."

I thought back over past adventures, the lunatic

asylum keeper, the butcher's young man, the suave doctor, all the same man, and all totally unlike each other.

"It's amazing," I said at last. "Everything fits in. Savaronoff had an inkling of the plot, and that's why he was so averse to playing the match."

Poirot looked at me without speaking. Then he

turned abruptly away, and began pacing up and down.

"Have you a book on chess by any chance, mon

amiV he asked suddenly.

"I believe I have somewhere."

It took me some time to ferret it out, but I found it at last, and brought it to Poirot, who sank down in a chair and started reading it with the greatest attention.

In about a quarter of an hour the telephone rang. I

answered it. It was Japp. Ivan had left the flat, carrying a large bundle. He had sprung into a waiting taxi, and

the chase had begun. He was evidently trying to lose his pursuers. In the end he seemed to fancy that he had

done so, and had then driven to a big empty house at

Hampstead. The house was surrounded.

I recounted all this to Poirot. He merely stared at me

as though he scarcely took in what I was saying. He held out the chess book.

"Listen to this, my friend. This is the Ruy Lopez

opening. 1 P-K4, P-K4; 2 Kt-KB3, Kt-QB3; 3BKt5;

Then there comes a question as to Black's best third

move. He has the choice of various defences. It was

White's third move that killed Gilmour Wilson, 3BKt5.

Only the third move--does that say nothing to you?" I hadn't the least idea what he meant, and told him

so.

"Suppose, Hastings, that while you were sitting in

this chair, you heard the front door being opened and

shut, what would you think?"

"I should think some one had gone out, I suppose."

"Yes--but there are always two ways of looking

at things. Some one gone out--some one come w--two

totally different things, Hastings. But if you assumed

the wrong one, presently some little discrepancy would

creep in and show you that you were on the wrong

track."

"What does all this mean. Poirot?"

Poirot sprang to his feet with sudden energy.

"It means that I have been a triple imbecile. Quick, quick, to the flat in Westminster. We may yet be in

time."

We tore off in a taxi. Poirot returned no answer to my