Jacob Kanon, a New York detective, is devastated by the brutal murder of his daughter and her husband during their honeymoon in Europe. Desperate to find the killer, he travels to various European cities where similar gruesome murders have taken place. Each crime scene is marked by a postcard sent to a local journalist prior to the killings, featuring stylized images and cryptic messages. Kanon teams up with Scandinavian journalist Dessie Lombard, who has received one such postcard and reluctantly agrees to help him track down the elusive serial killer responsible for these atrocities.

As Jacob and Dessie delve deeper into the investigation, they uncover a pattern linking the murders to famous artworks and historical landmarks. With each clue, they edge closer to identifying the perpetrator, despite facing numerous obstacles and red herrings. The pair navigates through a web of deceit, encountering a range of characters that either help or hinder their progress. Pressured by the mounting body count and haunted by his personal loss, Jacob's determination pushes him to the brink of obsession as he races against time to prevent further killings.