Ruth’s father, an American millionaire who enlists Poirot to investigate his daughter’s death and her missing jewel.

Rufus Van Aldin’s secretary, who joins his employer in persuading Poirot to take responsibility for investigating the case.

Ruth Kettering’s maid, who reports seeing an unidentified man inside her employer’s compartment during the journey.

Ruth’s lover, whom the police suspect of killing her and stealing the ruby, though Poirot doubts that conclusion.

A Parisian dancer and Derek’s lover, she is aboard the train with him and becomes vengeful after being spurned.

Katherine’s titled cousin and the owner of a Riviera villa, where Katherine stays during her time in the region.

Lady Rosalie Tamplin’s daughter, distinguishing her from Rosalie’s much younger husband in Katherine’s Riviera household.