First published in 1926, this is an individual Poirot story. Lily Margrave is the paid companion to Lady Atwell. She tells Poirot that Lady Atwell's husband, Sir Reuben Atwell, was found murdered in the Tower Room at his house, Mon Repos. His nephew, Charles Leverson, has been arrested for the murder - having been heard arguing with his uncle late at night by the butler, but Lady Atwell suspects her husbands secretary, Owen Trefusis. Intrigued, M. Poirot goes to the scene of the crime to investigate.
This excellent story has all of Agatha Christie's trademarks. There is the country house, an excellent cast of suspects - the brother just returned from Africa, the quiet secretary, the wife who was once an actress, and more. Poirot is though, the cat by the mousehole, as he puts it. When his grand denouncement comes, he has been patient and, of course, solved the murder. For anyone who wishes to perhaps try Christie, these stories are a great way of sampling her work.