The Postcard Killings follows a New York detective searching for the person responsible for her daughter and son-in-law’s grisly murders. Assisted by a Scandinavian journalist, he discovers similar murders across Europe. The standout thing that links all killings is a postcard that appears in the local newspaper before each new victim is found. 

The Postcard Killings is not based on a true story; it is adapted from a crime novel

The Postcard Killings is based on a fictional novel titled The Postcard Killers by James Patterson and Liza Marklund. James is an award-winning writer whose works have inspired several on-screen productions. Marklund, on the other hand, is a journalist-turned-writer. 

Contrary to what some sources on the web claim, The Postcard Killings is not based on J. Frank Hickey, a serial killer from the late 1800s and early 1900s popularly known as The Postcard Killer. Hickey earned the moniker because he sent lengthy correspondences about his crimes to reporters and the police.