Murder by Death (1976)

Five diverse, infamous private eyes, including Sam Diamond (Peter Falk), Sidney Wang (Peter Sellers) and Jessica Marbles (Elsa Lanchester), are invited to the mysterious Lionel Twain's castle for a dinner party. There, they are told that Twain plans an unsolvable murder in the house at midnight -- and he will pay $1 million to the one who determines the killer. But when Twain's blind butler, Bensonmum (Alec Guinness), dies long before the deadline, the stakes go up for the trapped sleuths.