Cujo is a friendly huge St. Bernard in the age of 5, the dog of Camber family in Castle Rock, Maine. One day by accident, while chasing a rabbit, he gets bitten by a bat and gets rabies from it. While he slowly loses his mind, we get to watch the everyday life and problems of the Camber and the Trenton family in Castle Rock. But that doesn't matter anymore when the monster starts to wreak havoc and now everyone around him is in danger, and only care about one sole thing: to survive.