Heading for the French Rivieria, recently retired detective Hercule Poirot boards Le Train Bleu in London. This luxury trip, however, quickly turns south—in more ways than one. When the train arrives in Nice, France, American heiress Ruth Kettering is found murdered, and the Heart of Fire ruby that just came into her possession from her father has vanished in an apparent robbery. Add in a jilted husband, a secret lover, and a supposed curse on the missing gemstone, and it's a mystery that just might lure Poirot from his supposed retirement.