Out fishing one day, painter John Hammond and his son Chris come across Bert Hillman, the foreman of a local ranch. He and his ranch hand are searching for a wild dog that killed one of their sheep. They find the animal and kill it, along with one of its puppies, but after they leave Hammond and his son discover another puppy still alive. They take it home and call it Rocky. John believes that a dog descended from sheep-killers will himself become a sheep-killer someday, but he gives his son a chance to raise and train the dog, hoping that he can train the killer instinct from it. Unfortunately, local farmers have reported an epidemic of sheep-killings, and they suspect that Rocky is responsible for them.