The Mitford Murders by Julian Fellowes

Set in 1920s England, the novel follows a murder that shatters the placid world of an aristocratic household and draws a determined investigator into the private lives of the Mitford family; as he digs beneath polished surfaces he uncovers rivalries, romantic entanglements and political tensions that reveal how fragile respectability can be. The story blends atmospheric period detail and social observation with a classic whodunit structure, charting both a search for a killer and a portrait of a family and era on the verge of change.