A young widow is left in sole possession of her late husband's fortune, and her brother refuses to share it with her in-laws - so they enlist Poirot to try to prove that the widow's missing first husband might not be dead after all.

When a man disinherits his sole beneficiary and bequeaths his wealth to others just prior to his death, Poirot is called in to investigate.

The enigmatic, sinister Mr. Shaitana, one of London's richest men, invites 8 guests, 4 of them possible murderers and 4 'detectives' to his opulent apartment.

Poirot investigates the brutal murder of an American heiress and the theft of a fabulous ruby on the Blue Train between Calais and Nice.