A Haunting in Venice begins by following a thirteen-year-old girl named Joyce Reynolds, who is at a Halloween party at a small village in England called Woodleigh Common. Joyce claims to have once witnessed a murder, but her assertion is largely ignored by the partygoers until she is found dead later that evening by fellow partygoers after being drowned in an apple-bobbing tub. One of the partygoers, a man named Ariadne Oliver, enlists the help of his friend, Detective Hercule Poirot, to solve the murders.
As Poirot delves into the case, he learns about a past unsolved murder in the village that shares a lot of similarities with Joyce's murder. He discovers the murder of a woman named Lesley Ferrier, who died by strangulation. In fact, he starts to think that Joyce witnessed Lesley's murder. Through his investigation, Poirot identifies several potential suspects, including Rowena Drake, a respected village figure; Mrs. Goodbody, an older woman who likes to gossip; and Michael Garfield, an enigmatic and attractive gardener.
Poirot discovers that another young girl, Miranda Butler, may have also witnessed the same murder as Joyce. Over time, Poirot comes to realize that Lesley (and later, Joyce) was murdered because of an inheritance that was meant for Miranda. The murderer wanted nothing more than to get their hands on the money and would stop at nothing to get it, reflecting their evil heart.
After a relatively lengthy investigation, Poirot confronts the killer in a fairly dramatic way. He reveals the murderer to be Michael Garfield, the gardener and one of his prime suspects. Garfield admits that he was involved in a romantic relationship with Lesley Ferrier. He killed Lesley to keep her quiet about Miranda's paternity. He also killed Joyce to compel her silence because he feared she witnessed Lesley's murder. In the end, Garfield is arrested and presumably tried for his crimes, showing that karma exists and that, in one way or another, people are held accountable for their actions.
Throughout the novel, the innocence of a Halloween is often contrasted with the darkness of human behavior. Although many characters in the novel appear to be harmless beneath the surface, they oftentimes have ulterior, usually negative or harmful, intentions. Poirot himself is the opposite of many characters in the novel: he is methodical and very direct in his intentions and motives.
Poirot's indirect investigative approach highlights the importance of observation and understanding human nature in detective work. Poirot has a keen observational eye, which gives Poirot additional, richer characterization. Poirot, being from Belgium, also allows him to view different situations and people without the bias of being tied to the community in which he is investigating a crime.
The novel also explores the intricacies of a seemingly close-knit community. Christie exposes the facades that individuals create to keep up appearances. She also unravels how a single event can deconstruct that facade and destroy an entire community.
