An invitation to "dinner and a murder" has been sent by eccentric millionaire Lionel Twain (Truman Capote) to five of the world's most famous private detectives: Belgium's Milo Perrier (James Coco); private eye Sam Diamond (Peter Falk) from the U.S.; England's famous female sleuth Jessica Marbles (Elsa Lanchester); the inscrutable Sidney Wang (Peter Sellers); and the urbane Dick and Dora Charleston (David Niven and Maggie Smith). Attended by a house staff that includes his blind butler, Benson-mum (Sir Alec Guiness), and a deaf-mute cook, Yetta (Nancy Walker), Twain reveals that someone in the room will be stabbed to death twelve times at midnight and then challenges the assembled criminologists to solve the crime - for one million dollars tax free and the title of champion detective. With the doors locked and windows bolted so that no one can leave, rooms appear and disappear, as does a mysterious corpse. Racing against time, each detective uses their deductive skills to outwit the fiendishly clever host... as the clock strikes twelve...