Now retired and living in self-imposed exile in the world's most glamorous city, Poirot reluctantly attends a seance at a decaying, haunted palazzo. When one of the guests is murdered, the detective is thrust into a sinister world of shadows and secrets.

A group of friends and family meet on an island just outside of Seattle to celebrate a wedding. On the island, which is famous for a streak of unsolved murders that occurred seven years ago, suspense ensues when one by one they end up dead. Has the killer returned or is someone else to blame?

Guy Haines, a tennis star who hates his wife, is approached on a train by a stranger, Bruno Anthony, who hates his father. Anthony offers a plan: each could kill the other's victim. No motive, no clue would link the two murders save the casual meeting of strangers on a train.

Detective William Murdoch and his wife, Dr. Julia Ogden, plan their dream home; Constable Crabtree faces dire consequences for his decisions; and Dr. Emily Grace experiences a personal crisis. Meanwhile, Inspector Brackenreid endures an eccentric houseguest, and a new morgue cleaner turned lab attendant brings fresh blood to the team.