John Dickson Carr 
Emperor’s Snuff-Box [EPUB ebook] 

The scene is a fashionable French seaside resort; the witness, Eve Neill, is looking out of her window in the early hours of the morning when she sees the battered body of her prospective father-in-law in the room opposite.By Eve’s side is her ex-husband, who has attempted to force his unwelcome attentions on her. How can Eve tell the police what she saw when disclosing whom she was with might jeopardise her own impending marriage?Suspicion falls on casual thieves, on the family and on various acquaintances, but the complicated 'locked-room’ case is eventually solved by Dr Dermot Kinross, a detective who becomes emotionally involved …