The Hollow, by Agatha Christie

A week end house party at The Hollow, home of Sir Henry Angkatell and his wife Lucy, turns into a nightmare when tragedy strikes. Among the guests are three of the Angkatell cousins, Edward, Midge and Henrietta- Edward is in love with Henrietta and Midge is in love with Edward. Also present are Dr John Cristow and his wife, Gerda. Imagine Cristow’s shock when he finds not only his wife and mistress, Henrietta, under the same roof, but also his ex-mistress, the actress, Veronica Craye. The scene is set for murder. How fortunate that there is a detective on hand to help solve the mystery.