While on vacation at a resort hotel in the West Indies, Miss Marple correctly suspects that the apparently natural death of a retired British major is actually the work of a murderer planning yet another killing.

A friend of Miss Marple's sees a woman being strangled in a passing train. When police cannot find a body and doubt the story, Miss Marple enlists professional housekeeper, Lucy Eyelesbarrow, to go undercover.

Faced with two false confessions and numerous suspects after a despised civil magistrate is found shot in the local vicarage, Detective Inspector Slack reluctantly accepts help from Miss Marple.