Cujo is a novel by Stephen King that was first published in 1981. The book tells the story of a friendly Saint Bernard dog named Cujo, who turns into a ferocious killer after being bitten by a rabid bat. The story is set in a small town in Maine and follows the lives of several characters, including the owners of Cujo and a mother and son who become trapped in their car by the rabid dog.

The book begins by introducing the reader to the various characters and their lives. Vic and Donna Trenton are a married couple with a young son named Tad. They are experiencing marital problems, which are compounded by Vic's infidelity. Meanwhile, Joe Camber and his family are the owners of Cujo, a friendly and beloved pet. However, when Cujo is bitten by a rabid bat, his behavior changes drastically, and he becomes a vicious killer.

As the story progresses, Donna and Tad find themselves stranded in their car, unable to escape the wrath of the rabid dog. Meanwhile, Vic is struggling with guilt over his infidelity and must come to terms with his love for his family. The story builds to a climactic and gruesome showdown between Cujo and the trapped mother and son.

The novel explores themes of infidelity, the breakdown of the family unit, and the consequences of our actions. It also delves into the nature of fear and the primal instincts that can take over when we are pushed to the brink.

Overall, Cujo is a gripping and intense novel that is sure to keep readers on the edge of their seats. King's masterful storytelling and vivid descriptions of both the characters and the setting create a world that is both familiar and terrifying. The book has been adapted into a film, a comic book series, and a stage play, attesting to its lasting popularity and cultural significance.