When his teenage son Tommy is found murdered in the town of Northfield, John Cooley sets out to avenge the boys death. John is a religious fanatic who believes he is on a mission from God. When he finds a piece of car headlight at the murder scene, he seeks out and kills the car's original owner Frency La Font and an elderly librarian who had some connection to the car. With all the murders, the residents of Northfield are unstandably shaken. They demand that Sheriff Will Pearce solve the case. Unfortunately, Pearce's girlfriend Susan Marsh falls under Cooley's suspicions since she bought the car from La Font. His attempt to kill her, however, is foiled at the last second by the timely arrival of Sheriff Pearce. Pearce explains that La Font murdered Tommy and confessed to it in his last will and testament.

Le fils de John Cooley est mort à la suite d'un accident de voiture. On l'a écrasé. La personne qui l'a tué s'est enfui et a laissé le corps près d'un fossé. Bientôt de nombreux autres accidents ont lieu. Le shérif Pearce est persuadé qu'il s'agit d'un tueur en série.