After Miss Marple's friend witnesses a murder in a railway carriage running parallel to her own, Miss Marple engages a resourceful young woman to investigate. The search leads to a decrepit estate, where they suspect the body was dumped. But the seemingly innocent family who lives there have secrets of their own.

At an estate turned reformatory school, Miss Marple visits her old school chum Carrie Louise. When Carrie Louise's dear stepson is killed, the discontent family is only the beginning as there are literally hundreds of suspects!