Sherlock Holmes is called to investigate a series of strange events at Three Gables, a house in Harrow Weald. The elderly owner, Mrs Maberley, has been receiving threats from a mysterious man who wants to buy her house and all its contents. Holmes soon discovers that the man is after a manuscript written by Mrs Maberley's son, Douglas, who recently died in Rome. The manuscript is a lurid novel in which Douglas inserts himself as a character. Holmes deduces that the mysterious man is someone who wants to destroy the manuscript, and he sets out to find out who it is.