Caught in a loveless marriage, Dr. John Winnington (Ronald Howard) can’t stop himself from falling for his wife’s (Mary Laura Wood) younger sister, Christine (Olga Edwardes). But when he suddenly becomes the prime suspect in his wife’s tragic murder, John relies on his friend Eric (John Bentley) to clear his name.

Lord Peter Wimsey, an amateur detective, marries a mystery novelist, Harriet Vane. The newly-weds set out for a honeymoon to Harriet's old family cottage. They end up investigating a murder case.

Captain Jeroboam Barker-Rynde (Terry Thomas) comes to a country hotel to assist a wealthy widow. He endures a nature cure diet and exercises under Rumbelow (Eric Sykes). When the widow is poisoned, Barker Rynde and Rumbelow join forces to win a reward offered by hotel manager Crossley (Dennis Price). Crossley is next murdered, and the clues point to the original criminal.