"The police are not so sure that it was--heart failure, mademoiselle."

The girl gave a terrified gesture.

"It was true then," she cried. "Ivan was right."

"Who is Ivan, and why do you say he was right?"

"It was Ivan who opened the door to you--and he

has already said to me that in his opinion Gilmour

Wilson did not die a natural death--that he was poisoned by mistake."

"By mistake."

"Yes, the poison was meant for my uncle."

She had quite forgotten her first distrust now, and

was speaking eagerly.

"Why do you say that, mademoiselle. Who should

wish to poison Dr. Savaronoff?"

She shook her head.

"I do not know. I am all in the dark. And my uncle, he will not trust me. It is natural, perhaps. You see, he hardly knows me. He saw me as a child, and not since

till I came to live with him here in London. But this

much I do know, he is in fear of something. We have

many secret societies in Russia, and one day I overheard something which made me think it was of just such a

society he went in fear. Tell me, monsieur"--she came a step nearer, and dropped her voice--"have you ever

heard of a society called the 'Big Four'?"

Poirot jumped nearly out of his skin. His eyes

positively bulged with astonishment.

"Why do you--what do you know of the Big Four,

mademoiselle?"

"There is such an association, then! I overheard a

reference to them, and asked my uncle about it afterwards. Never have I seen a man so afraid. He turned all

white and shaking. He was in fear of them, monsieur, in

great fear, I am sure of it. And, by mistake, they killed the American, Wilson."

"The Big Four," murmured Poirot. "Always the Big Four! An astonishing coincidence, mademoiselle, your

uncle is still in danger. I must save him. Now recount to me exactly the events of that fatal evening. Show me the chess-board, the table, how the two men sat--everything." She

went to the side of the room and brought out a

small table. The top of it was exquisite, inlaid with

squares of silver and black to represent a chessboard.

"This was sent to my uncle a few weeks ago as a present, with the request that he would use it in the next

match he played. It was in the middle of the room-so." Poirot examined the table with what seemed to me

quite unnecessary attention. He was not conducting the

inquiry at all as I would have done. Many of his questions seemed to me pointless, and upon really vital matters

he seemed to have no questions to ask. I concluded

that the unexpected mention of the Big Four had thrown

him completely off his balance.

After a minute examination of the table and the exact

position it had occupied, he asked to see the chessmen.

Sonia Daviloff brought them to him in a box. He examined one or two of them in a perfunctory manner.