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, Maggie Smith).