Watch Agatha Christie's Poirot: Hallowe'en Party

Wholesome fun at Woodleigh Commons turns harrowing when a children's Halloween party ends in the murder of 13-year-old Joyce Reynolds. Poirot is summoned by an old acquaintance, crime novelist Ariadne Oliver (Zoe Wanamaker, My Family), to help in the investigation. He seizes on a clue: immediately before her death, Joyce had boasted of having witnessed a murder several years before, although she didn't realize it was a murder at the time. Although everyone pooh-poohs her claim, Poirot knows that "old sins cast long shadows."