Mort Rainey is a recently divorced writer who suffered a psychotic break after discovering that his wife, Amy, was having an affair. One day, after suffering from a particularly harmful depression and writer's block, Mort is confronted by a dairy farmer from Mississippi called John Shooter who claims that Mort stole his story called "Sowing Season" and published it in his story collection, Everybody Drops the Dime. Mort compares the two stories, originally believing Shooter to be a whackjob or someone looking for lawsuit money, but then realizes that the two stories are shockingly similar. After realizing that Shooter's story was published first, Mort realizes that Shooter isn't lying, but assumes it to be a mere coincidence. However, Shooter slowly becomes more agressive, murdering Mort's own dog as well as several people and threatening those close to Mort, including his ex-wife. Mort slowly realizes more similarities between him and Shooter, and attempts to cover up Shooter's murders while his own sanity slowly starts to unravel. At the end, after Shooter burns down his cabin, it is revealed that Shooter never existed at all; he was really a figment of Mort's own imagination. Mort went insane after his wife divorced him and created the character of Shooter after the stress of discovering his wife's affair. After Amy arrives, Mort kills her and reveals that "Shooter" is merely "shoot her" combined. After killing Amy and her lover, Ted, he recovers from his writer's block and becomes himself again. After the town sheriff informs him that he is now the prime suspect in their deaths, Mort remained calm, knowing that burying the bodies in his corn garden will quickly decompose the bodies by taking the nutrients away from them.
The book's ending is more bittersweet. The book mainly stays the same as the film except for the ending. After Mort tries to kill Amy and Ted, he is shot to death by local police. Afterwards, Amy returns to Mort's house and discovers Shooter's hat. After this, John Shooter actually arrives and retrieves his hat, and Amy remarks that Mort created a character so vivid that he actually came to life.