curry before handing it over to be analysed. He gives his version of the conversation with the old man, and mentions the strychnine injection casually, in case the mark

of the hypodermic needle is noticed. Suspicion at once is divided between accident and the guilt of Ah Ling owing

to the poison in the curry."

"But Dr. Quentin cannot be Number Four?"

"I fancy he can. There is undoubtedly a real Dr.

Quentin who is probably abroad somewhere. Number

Four has simply masqueraded as him for a short time.

The arrangements with Dr. Bolitho were all carried out

by correspondence, the man who was to do locum originally having been taken ill at the last minute."

At that minute, Japp burst in, very red in the face.

"You have got him?" cried Poirot anxiously.

Japp shook his head, very out of breath.

"Bolitho came back from his holiday this morning

—recalled by telegram. No one knows who sent it. The

other man left last night. We'll catch him yet, though." Poirot shook his head quietly.

"I think not," he said, and absent-mindedly he drew a big 4 on the table with a fork.

The Problem

Poirot and I often dined at a small restaurant in Soho.

We were there one evening, when we observed a friend

at an adjacent table. It was Inspector Japp, and as there was room at our table, he came and joined us. It was

some time since either of us had seen him.

"Never do you drop in to see us nowadays," declared Poirot reproachfully. "Not since the affair of the Yellow Jasmine have we met, and that is nearly a month

ago."

"I've been up north--that's why. How are things

with you? Big Four still going strong--eh?"

Poirot shook a finger at him reproachfully.

"Ah! you mock yourself at me--but the Big Four-they exist."

"Oh! I don't doubt that--but they're not the hub of the universe, as you make out."

"My friend, you are very much mistaken. The

greatest power for evil in the world to-day is this 'Big Four.' To what end they are tending, no one knows, but

there has never been another such criminal organisation. The finest brain in China at the head of it, an

American millionaire, and a French woman scientist as

members, and for the fourth--"

Japp interrupted.

"I know--I know. Regular bee in your bonnet over it all. It's becoming your little mania, Moosior Poirot.

Let's talk of something else for a change. Take any interest in chess?"

"I have played it, yes."

"Did you see that curious business yesterday? Match between two players of world-wide reputation, and one

died during the game?"

"I saw a mention of it. Dr. Savaronoff, the Russian champion, was one of the players, and the other, who

succumbed to heart failure, was the brilliant young

American, Gilmour Wilson."

"Quite right. Savaronoff beat Rubinstein and became Russian champion some years ago. Wilson is said to be

a second Capablanca."

"A very curious occurrence," mused Poirot. "If I mistake not, you have a particular interest in the