After traveling on the Blue Train from Calais to Nice, Hercule Poirot is pressed into service to help solve the murder of heiress Ruth Kettering who is found savagely beaten in her compartment.

Hercule Poirot finds himself trying to solve the mystery of the Cloade family

On holiday in Jerusalem, Poirot hears about an archaeological expedition to Syria led by the eccentric Lord Boynton and his son Leonard, who believe they are on the track of the head of St John the Baptist. Drawn to visit the dig, Poirot meets Boynton's dominating, fabulously rich, American-born second wife. However, events are overtaken by the discovery of Lady Boynton's dead body and revelations about her fortune.

In an effort to recover his confidence after a rare professional failure, Poirot sets off for the Swiss Alps in pursuit of a missing maid.