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.

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.