When aging sleuth Miss Marple (Margaret Rutherford) witnesses a murder through the window of her passing train car, she alerts the authorities. Unfortunately, the police are hesitant to take the word of an old lady in lieu of an actual body. Taking matters into her own hands, Marple gets a job as a maid at Ackenthorpe Hall, where she believes the murder took place. There, she must match wits with blowhard Luther Ackenthorpe (James Robertson Justice) if she wants to solve the mystery.