After the murder at the séance, Poirot is approached by the victim's sister, who suspects that her brother's death was not a random act of violence but instead part of a larger conspiracy. Poirot reluctantly agrees to investigate, drawing him into a web of deceit and betrayal that reaches to the highest echelons of society.
As Poirot delves deeper into the case, he discovers a series of interconnected mysteries surrounding the palazzo, including a tragic love affair, a secret society, and a long-forgotten treasure. With the help of a local journalist and a young apprentice, Poirot races against time to uncover the truth before he becomes the killer's next victim.
As the investigation unfolds, Poirot finds himself facing his own demons, including the ghosts of his past and the realization that his own mortality is catching up to him. With the clock ticking and danger around every corner, Poirot must use all his wits and experience to solve the case and bring the killer to justice.