Its structure includes a prologue, epilogue, and three main parts each with their own chapters (which each have their own segments). The book was the second best-selling fiction book of 1989, and was adapted into a feature film directed by horror icon George A. Romero released in 1993, which spawned its own video game adaption.
The novel was written, in part, as a commentary on King's pseudonym Richard Bachman. The book was written after King was revealed to be behind the pen name, and was written in Bachman's darker style. The novel's plot is symbolic to how King felt about the debacle, featuring an author who's scared of his own violent pseudonym who comes to life and acts as an unwelcome guest. Because of this, The Dark Half is seen as Bachman's epitaph.
Thad Beaumont is an author and recovering alcoholic who lives in the town of Ludlow, Maine. Thad's own books – cerebral literary fiction – are not very successful. However, under the pen name "George Stark", he writes highly successful crime novels about a violent killer named Alexis Machine. When Thad's authorship of Stark's novels becomes public knowledge, Thad and his wife, Elizabeth, decide to stage a mock burial for his alter ego at the local cemetery, which is featured in a People magazine article. Stark's epitaph says it all: "Not A Very Nice Guy".
Stark, however, emerges from the mock grave as a physical entity, complete with the personality traits that Thad exhibited while writing as Stark, such as drinking heavily and smoking Pall Mall cigarettes. He then goes on a killing spree, gruesomely murdering everyone he perceives responsible for his "death" – Thad's editor, agent, and the People interviewer, among others. Thad, meanwhile, is plagued by surreal nightmares. Stark's murders are investigated by Alan Pangborn, the sheriff of the neighboring town of Castle Rock, who finds Thad's voice and fingerprints at the crime scenes. This evidence, and Thad's unwillingness to answer his questions, causes Pangborn to believe that Thad – despite having alibis – is responsible for the murders. Later, it is discovered that George Stark has the same fingerprints as Thad Beaumont, a clue to the twinship he and Thad share.
Thad eventually discovers that he and Stark share a mental bond, and begins to find notes from Stark written in his own handwriting. The notes tell Thad what activity Stark has been engaging in. Observing his son and daughter, Thad notes that twins share a unique bond. They can feel each other's pain and at times appear to read the other's mind. Using this as a key to his own situation, he begins to discover the even deeper meaning behind himself and Stark.
Pangborn eventually learns that Thad had a twin. The unborn brother was absorbed into Thad in utero and later removed from his brain when the author was a child. He had suffered from severe headaches and it was originally thought to be a tumor causing them. The neurosurgeon who removed it found the following inside: part of a nostril, some fingernails, some teeth, and a malformed human eye. This leads to questions about the true nature of Stark, whether he is a malevolent spirit with its own existence, or Thad himself, manifesting an alternate personality. Thad eventually vanquishes Stark, but the book ends on an unhappy note with Thad's wife having serious doubts about the future of their relationship: she is appalled that Thad not only created Stark (if unintentionally), but that a part of him liked Stark.
The film is faithful in many regards, but there was several key changes were made. The biggest of these changes were George Stark's appearance and attributes. His blonde hair was changed to black, and his overall stature is more similar to Thad's. While his quiet and nimble ways of killing and maneuvering remained, his heightened sense of hearing did not. Stark's biodegrading was lessened, possibly due to budgetary constraints. Thad's personality changed in the beginning of the film, where he acted slightly psychopathic (probably to make the audience suspect that he was the true perpetrater). The character of Rawlie Delesseps also changed, from a man to a woman with roughly the same characterization intact. The only difference is a change in first name (from Rawlie to Reggie) and a bigger role as the source of exposition. Clawson, instead of being a faithful fan of both names who noticed the connection, was a random lowlife who caught wind of a staff slip-up. His method of contacting Thad changed from writing a letter to a confrontation during one of Thad's classes at the university. The character of Homer Gamauche was changed from a chance killing to intentional.
Key events were also changed, such as the order of events surround Thad's run from his police protection. Instead of trying to find George Stark ,after his family was taken, he avoids the police to speak with Dr. Pritchard, which is a duty handled by Pangborn originally. Pangborn's importance in the ending was also downplayed, he arrived much later than in the novel. The whistle and Thad's control of the birds was taken away, making Stark's forceful return by the Sparrows seem inconsequential to any outside action. This in turn changes the climactic confrontation into symbolic fist fight between the two struggling halves. The film ends abruptly as Stark is taken into shifting red clouds, avoiding the ambiguous ending.
The audiobook version of The Dark Half is read by Grover Gardner.