The Fourth Man by Agatha Christie

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The Fourth Man is a short story, written by Agatha Christie. It is about a night train journey of Canon Parfitt. In his first class carriage he is reacquainted with Sir George Durand, a famous lawyer. A third man in the carriage introduces himself as Dr Campbell Clark, an eminent physician who is an expert on conditions of the mind. There is a fourth man with them who appears to be asleep.