The Mystery of the Blue Train

on examining the facts carefully, I noted two things. First, that by a curious coincidence he, too, had been exactly two months in your service. Secondly, his initial letter was the same⁠—‘K.’ Supposing⁠—just supposing⁠—that it was his cigarette-case which had been found in the carriage. Then, if Ada Mason and he were working together, and she recognised it when we showed it to her, would she not act precisely as she had done? At first, taken aback, she quickly evolved a plausible theory that would agree with Mr. Kettering’s guilt. Bien entendu, that was not the original idea. The Comte de la Roche was to be the scapegoat, though Ada Mason would not make her recognition of him too certain, in case he should be able to prove an alibi. Now, if you will cast your mind back to that time, you will remember a significant thing that happened. I suggested to Ada Mason that the man she had seen was not the Comte de la Roche, but Derek Kettering. She seemed uncertain at the time, but after I had got back to my hotel you rang me up and told me that she had come to you and said that, on thinking it over, she was now quite convinced that the man in question was Mr. Kettering. I had been expecting something of the kind. There could be but one explanation of this sudden certainty on her part. After my leaving your hotel, she had had time to consult with somebody, and had received instructions which she acted upon. Who had given her these instructions? Major Knighton. And there was another very small point, which might mean nothing or might mean a great deal. In casual conversation Knighton had talked of a jewel robbery in Yorkshire in a house where he was staying. Perhaps a mere coincidence⁠—perhaps another small link in the chain.”

“But there is one thing I do not understand, Monsieur Poirot. I guess I must be dense or I would have seen it before now. Who was the man in the train at Paris? Derek Kettering or the Comte de la Roche?”

“That is the simplicity of the whole thing. There was no man. Ah⁠—mille tonnerres!⁠—do you not see the cleverness of it all? Whose word have we for it that there ever was a man there? Only Ada Mason’s. And we believe in Ada Mason because of Knighton’s evidence that she was left behind in Paris.”

“But Ruth herself told the conductor that she had left her maid behind there,” demurred Van Aldin.

“Ah! I am coming to that. We have Mrs. Kettering’s own evidence there, but, on the other hand, we have not really got her evidence, because, Monsieur Van Aldin, a dead woman cannot give evidence. It is not her evidence, but the evidence of the conductor of the train⁠—a very different affair altogether.”

“So you think the man was lying?”

“No, no, not at all. He spoke what he thought to be the truth. But the woman who told him that she had left her maid in Paris was not Mrs. Kettering.”

Van Aldin stared at him.

“Monsieur Van Aldin, Ruth Kettering was dead before the train arrived at the Gare de Lyon. It was Ada Mason, dressed in her mistress’s very distinctive clothing, who purchased a dinner basket and who made that very necessary statement to the conductor.”

“Impossible!”

“No, no, Monsieur Van Aldin; not impossible. Les femmes, they look so much alike nowadays that one identifies them more by their clothing than by their faces. Ada Mason was the same height as your daughter. Dressed in that very sumptuous fur coat and the little red lacquer hat jammed down over her eyes, with just a bunch of auburn curls showing over each ear, it was no wonder that the conductor was deceived. He had not previously spoken to Mrs. Kettering, you remember. True, he had seen the maid just for a moment when she handed him the tickets, but his impression had been merely that of a gaunt, black-clad female. If he had been an unusually intelligent man, he might have gone so far as to say that mistress and maid were not unlike, but it is extremely unlikely that he would even think that. And remember, Ada Mason, or Kitty Kidd, was an actress, able to change her appearance and tone of voice at a moment’s notice. No, no; there was no danger of his recognising the maid in the mistress’s clothing, but there was the danger that when he came to discover the body he might realise it was not the woman he had talked to the night before. And now we see the reason for the disfigured face. The chief danger that Ada Mason ran was that Katherine Grey might visit her compartment after the train left Paris, and she provided against that difficulty by ordering a dinner basket and by locking herself in her compartment.”

“But who killed Ruth⁠—and when?”

“First, bear it in mind that the crime was planned and undertaken by the two of them⁠—Knighton and Ada Mason, working together. Knighton was in Paris that day on your business. He boarded the train somewhere on its way round the ceinture. Mrs. Kettering would be surprised, but she would be quite unsuspicious. Perhaps he draws her attention to something out of the window, and as she turns to look he slips the cord round her neck⁠—and the whole thing is over in a second or two. The door of the compartment is locked, and he and Ada Mason set to work. They strip off the dead woman’s outer clothes. Mason and Knighton roll the body up in a rug and put it on the seat in the adjoining compartment amongst the bags and suitcases. Knighton drops off the train, taking the jewel-case containing the rubies with him. Since the crime is not supposed to have been committed until nearly twelve hours later he is perfectly safe, and his