A A Milne (1882-1956)
The Red House Mystery (1922)
This novel is Golden Age detective story from the author of Winnie the Pooh.
http://en.wikipedia.org/wiki/The_Red_House_Mystery
“The Red House Mystery is a "Whodunit" mystery novel by A. A. Milne, published in 1922. It was Milne's only mystery novel; he is better known for his children's stories and poems.
The setting is bachelor Mark Ablett's English country house loaded with guests, including a British major, a wilful actress, and a young jock athlete. Mark's long-lost brother Robert, the black sheep of the family, arrives from Australia and is found murdered in a locked room. Mark Ablett has disappeared so Tony Gillingham and his friend Bill decide to investigate, progressing almost playfully through the novel while the clues mount up the theories abound.”