THE HOLLOW by Agatha Christie

An unhappy game of romantic "Follow My Leader" explodes into murder one weekend at The Hollow, home of Sir Henry & Lucy Angkatell. Dr John Cristow is at the centre of the trouble, for at The Hollow are Henrietta (his mistress), Veronica (his ex-mistress), and Gerda (his wife). To further complicate matters, also present is Edward - in love with Henrietta, and Midge - in love with Edward. Veronica ardently desires to marry Dr Cristow but although she succeeds in re-opening their "affaire", he refuses to divorce his wife. At this point, Veronica unwisely threatens that if she cannot have him, no-one else shall. Within minutes, Cristow is dead.

Nearly everyone has a motive to wish Cristow dead; most had the opportunity, but who actually committed the murder has to be discovered by Inspector Colquhoun and Sergeant Penny.