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 tress for two months. Certainly it did not seem as if she could have had anything to do with the crime since she had been left behind in Paris and Mrs. Kettering had been seen alive by several people afterwards, but"

Poirot leant forward. He raised an emphatic forefinger and wagged it with intense emphasis at Van Aldin.

"But I am a good detective. I suspect. There is nobody and nothing that I do not suspect. I believe nothing that I am told. I say to myself: how do we know that Ada Mason was left behind in Paris? And at first the answer to that question seemed completely satisfactory. There was the evidence of your secretary, Major Knighton, a complete outsider whose testimony might be supposed to be entirely impartial, and there was the dead woman's own words to the conductor on the train. But I put the latter point aside for the moment, because a very curious ideaan idea perhaps fantastic and impossiblewas growing up in my mind. If by any outside chance it happened to be true, that particular piece of testimony was worthless.

"I concentrated on the chief stumbling-block to my theory. Major Knighton's statement that he saw Ada Mason at the Ritz after the Blue Train had left Paris. That seemed conclusive enough, but yet, 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.' Supposingjust supposingthat it was his cigarette case which had been found in the carriage. Then, if Ada Mason and he were work