In the season two finale of Agatha Christie's Poirot , "Peril at End House," Hercule Poirot uncovers that Nick Buckley is the true killer, having staged multiple attempts on her own life to cover up murdering her cousin, Maggie, for an inheritance. Poirot exposes Nick and the accomplice forgers during a dramatic staged séance, leading to Nick's confession and subsequent suicide to avoid justice. You can watch the full episode on the PBS website or through Apple TV .