Walter Sparrow (Jim Carrey) is an animal control officer married to Agatha (Virginia Madsen); they have a son, Robin (Logan Lerman). At a bookstore, Agatha begins looking at a book called “The Number 23” written by Topsy Kretts. She later gives Walter the book as a birthday present.

Walter starts reading the book, noticing odd similarities between himself and the main character, a detective who refers to himself as “Fingerling”. Walter begins to have dreams of murdering Agatha. After one such dream he checks into a hotel where he stays up all night finishing the book, only to discover that it ends at chapter 22 with Fingerling about to commit suicide after murdering his lover…