The crime writer Ariadne Oliver attends a children's Halloween party at a large country house in the village of Woodleigh Common. One of the partygoers, a girl named Joyce Reynolds, boasts that she once witnessed a murder. Shortly afterwards, she is found drowned in an apple bobbing tub. Ms Oliver contacts her friend, the Belgian-born former police officer turned private detective Hercule Poirot, in the hope that he can find the murderer. Unlike almost everyone else, Poirot takes Joyce Reynolds' claim that she once saw a murder seriously and believes that it is the reason why she was killed. He soon finds out that several other people have died in mysterious circumstances in the village in recent years and gradually uncovers the sinister truth behind those deaths.