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 si looking for a murderer or a double-murderer...

A typical A. Christie story... however the idea is nice and the solution is interesting as always...