Despite not knowing him, the world's most famous detectives can't pass up the offer of a "dinner and murder" invitation from wealthy Lionel Twain (Truman Capote). Each has no idea until their arrival at Two Two Twain who else will be in attendance. Those detectives are: amateur sleuths and New York City socialites Dick (David Niven) and Dora Charleston (Dame Maggie Smith), accompanied by their pet terrier, Myron; Belgian detective Monsieur Milo Perrier (James Coco), accompanied by his chauffeur, Marcel (James Cromwell); Shanghainese Inspector Sidney Wang (Peter Sellers), accompanied by his Japanese adopted son, Willie Wang (Richard Narita); frumpish Brit Miss Jessica Marbles (Elsa Lanchester), accompanied by her invalid nurse, Miss Withers (Estelle Winwood); and San Francisco gumshoe Sam Diamond (Peter Falk), accompanied by his femme fatale sidekick, Tess Skeffington (Eileen Brennan). The dinner part of the invitation runs into problems due to the non-communication between Twain's blind butler, Jamesir Bensonmum (Sir Alec Guinness), and Twain's new deaf-mute and non-Anglophone cook, Yetta (Nancy Walker). On the murder side, the guests initially believe Twain will try to kill each of them. However, Twain eventually announces his rationale for the gathering: that one of the people at the dinner table will be murdered before midnight, and that Twain will consider himself the greatest detective if his guests, who are now trapped in the house until dawn, cannot figure out who committed the murder, that person also at the dinner table. If one does figure out who committed the crime, he or she will be the recipient of one million dollars and the exclusive rights to the story. So the guests anxiously await the stroke of midnight, with those still alive after that time trying to figure out motive and the opportunity to murder before the rise of dawn, and before the murderer has the opportunity to strike again on one or all of them.