At a Hallowe'en party, Joyce, a hostile thirteen-year-old, boasts that she once witnessed a murder. When no one believes her, she storms off home. But within hours her body is found, still in the house, drowned in an apple-bobbing tub. That night, Hercule Poirot is called in to find the evil presence. But first he must establish whether he is looking for a murderer or a double murderer ...