"The Red House Mystery" by A. A. Milne is a whodunnit published in 1922. When a black sheep brother arrives at an English country house and is found shot dead, the host mysteriously vanishes. An amateur detective visiting a friend decides to investigate, playing Sherlock Holmes while clues mount and theories multiply. Milne's only mystery novel became immediately popular, though it later sparked debate about the merits of Golden Age detective fiction and its preference for charming amateurs over professional investigators.