An announcement in the local paper states the time and place when a murder is to occur in Miss Blacklock's Victorian house. The victim is not one of the house's several occupants, but an unexpected and unknown visitor.

What follows is a classic Agatha Christie puzzle of mixed motives, concealed identities, a second death and a determined inspector grimly following the case's twists and turns. Fortunately, Miss Marple is on hand to provide the solution - at some risk to herself - in a dramatic final confrontation.