A stray dog infected with radiation stalks the family that adopted his puppies. The Yates family -- parents Brian and Jennifer, children Josh and Heather and dog Trixie -- move into a new home close to a nuclear power plant where stray dog Cerberus lives. Trixie runs off and mates with Cerberus, whose exposure to radiation has made him a crazed dog. When Trixie gives birth to her two puppies, she dies. Josh and Heather have never stopped looking for Trixie and find her and the puppies. They bury Trixie and take the puppies home, naming them Psycho and Scamp. Cerberus tracks the puppies to the Yates household and then to the vet, whom he attacks and kills. Biologist Janice Rifkin helps Josh investigate the killing and look for Psycho who disappeared after the murder.