While traveling from London to Kingfisher Hill to discretely investigate murder allegations against a wealthy client's wife, Hercule Poirot swaps seats with a nervous train passenger before a second killing is complicated by a series of impossible confessions.

Hercule Poirot is traveling by luxury passenger coach from London to the exclusive Kingfisher Hill estate. Richard Devonport has summoned the renowned detective to prove that his fiancée, Helen, is innocent of the murder of his brother, Frank. Poirot will have only days to investigate before Helen is hanged, and there is one condition: he must conceal his true reason for being there from the rest of the Devonport family. The coach is forced to stop when a distressed woman demands to get off, insisting that if she stays in her seat, she will be murdered. Although the rest of the journey passes without anyone being harmed, Poirot's curiosity is aroused, and his fears are later confirmed when a body is discovered with a macabre note attached. -- adapted from back cover