Hercule Poirot is visiting Istanbul, having solved a complex case for the British Army, when he witnesses an act of brutal justiceon the streets. Relieved when a new case calls him back to London, Poirot's old acquaintance Xavier Bouc, who is director of the Orient Express, secures him a last minute ticket. Among the eclectic range of passengers are Princess Dragomiroff and her nervous maid Hildegarde Schmidt, English Governess Mary Debenham and Swedish missionary Greta Ohlsson. During the journey Poirot is approached by ruthless American businessman Samuel Ratchett who offers him ten thousand dollars to watch his back but Poirot refuses. Could Ratchett be fearful of the Italian Antonio Foscarelli, English Colonel John Arbuthnot, pushy American Mrs Hubbard or Hungarian diplomat Count Andrenyi and his wife? Poirot awakes the following morning to find the train stuck in a snowdrift and Ratchett dead in his compartment, stabbed a dozen times. Aided by amateur sleuth Dr Constantine, Poirot examines the murder scene and finds a proliferation of clues pointing in opposite directions. He interviews those who last saw Ratchett alive: his manservant Edward Masterman, personal assistant, Hector MacQueen, and conductor Pierre Michel, before realising the true identity of Samuel Ratchett. The evidence seems to point to a mysterious assassin who got on and off the train but Poirot is convinced that the real answer lies in a tragic story from the past. Isolated by the snow and with civilisation falling apart Poirot makes a decision that will change his life forever.