An innocent children's Halloween party is being held in a small town near London, during the course of the party a child makes an innocuous remark about witnessing a murder some years back, she did not know at that time that it was murder but now she knows. The child is found murdered after the party ends. Did someone got spooked or did some malignant outsider step in the house and kill her? Ariadne Oliver, prolific mystery novel author and Poirot's friend was also present at the party and she believes that some malevolent person is behind the killing of the child. So, she goes to London to meet Poirot and once again Poirot has to use his little gray cells to solve this most perplexing murder.