Railway director and fellow Belgian Monsieur Bouc secures Poirot a last minute berth on the Orient Express, returning to England from Istanbul. Ratchett, an abrasive American businessman, traveling with his valet and male secretary, tries to secure Poirot's services as he fears that his life is in danger. Poirot turns him down, but the next morning, whilst the train is stuck in a snowdrift in Serbia, Ratchett is found stabbed to death. There is vague talk of a man seen fleeing the train, but many of the passengers in Poirot's compartment do not appear to know either Ratchett or each other, so what could the motive be? Poirot, assisted by Bouc and Dr. Constantine, attempts to find out.