While driving at night, aspiring actress Julie Sawyer (Kristy McNichol) accidentally runs over a white German shepherd. She takes the dog to a veterinarian and pays for its medical treatment, but is informed that the dog is unfit for adoption and will likely be put to sleep if handed over to the pound. Julie decides to keep the dog at her house until contacted by its owner. Concerned that Julie lives alone, her boyfriend, Roland Gray, encourages her to keep the animal as a guard dog. One night, a would-be rapist assaults Julie in her home. Jolted awake by the sounds of their struggle, the dog attacks the intruder, allowing Julie time to call the police.Several days later, the dog runs away, and Julie searches for it in vain, even checking the pound to see if the dog has been picked up or turned in. The following night the dog attacks and kills the driver of a street sweeper. The dog returns to Julie's house, blood streaked across its face. Julie cleans up the animal and fails to tell Roland about the state in which she found it.The following day Julie takes the dog with her to a studio lot where she is acting in a film. In the middle of a take, the dog attacks Molly, an actress playing a scene with Julie, severely harming her. Roland, now aware of the dog's violent behavior, tells Julie that this is an attack dog and orders her to have it put down before it claims another victim. Julie refuses and takes the dog to Noah's Ark, an animal training facility, where she seeks someone who can re-train the animal not to attack people. Mr. Carruthers (Burl Ives), one of the owners of the facility, informs her that there is nothing he can do.As Julie leaves the office, the dog breaks free of her grip and jumps a black handyman, but the animal is restrained before it can inflict serious injury. Carruthers heatedly tells Julie that her pet is a 'white dog,' trained by racists to assault black people. This explains the attacks on the sweeper driver and the actress, Molly, both of whom are black. Witnessing the dog's latest assault, the co-owner of Noah's Ark, a black animal trainer named Keys (Paul Winfield), takes it upon himself to recondition the German shepherd so that it no longer attacks black people. He also makes clear that the dog's condition is to be kept a secret.As he attempts to retrain the dog through a series of confrontations in a caged arena, Keys gradually reveals his history with white dogs and explains to Julie how they are created: white racists manipulate desperate black junkies into beating puppies until they learn to hate and attack black skin. Many animal trainers, Keys included, have tried to cure white dogs, but each time the dogs have proven unable to take the last step without snapping altogether and turning into indiscriminate attack dogs.One night, the dog breaks loose of its cage and escapes from the facility. The following day, while Keys searches around town, the dog chases a black pedestrian into an empty church and kills him. Keys subdues the dog after the attack, enters the church, and, with tears in his eyes, finds the man's corpse among the pews. When Keys returns to Noah's Ark and explains what happened, Julie immediately pleads for the dog to be killed before it takes the life of yet another innocent black person. Keys angrily retorts that as much as he'd like to shoot it, killing the dog would be nothing more than a short-term solution. Reconditioning is the only procedure that can prevent the creation of more white dogs in the future.After further training, the dog shows its first sign of improvement by willingly eating out of Keys' hand, an action that it initially refused to do. That night, as Keys, Julie and Carruthers hold a celebratory dinner to mark their first victory, they acknowledge that by keeping the nature of the dog hidden from the authorities, they are essentially accessories to murder. During their conversation, a police officer enters. Though they are worried that he may have found out about the dog, it turns out that he has only come to ask for directions. After he leaves, they conclude that in spite of what the authorities decree, what they are doing is right and humane.In the following weeks, the dog continues to make slight improvements until it is finally content around black people without turning to violence. Although Carruthers is confident that they are on the verge of victory, Keys reminds him that the dog is on the edge of a mental breakdown. Keys reluctantly calls Julie, telling her they can begin the "final test".On the way out of her house, Julie comes face-to-face with the dog's previous owner, an old man accompanied by his two granddaughters. After questioning the man and finding that he was responsible for creating the white dog, Julie refuses to return the animal and warns his granddaughters not to let him corrupt them as well.At Noah's Ark, Keys, Julie, and Carruthers stand in triangular formation in the caged arena. Keys beckons the dog in from outside, and it runs to Keys without attacking. Hearing Julie's voice, it runs to her as well, again showing no sign of violent behavior. However, upon seeing Carruthers, the dog springs and pins him to the ground. Here, Keys finally accepts that the animal's hatred cannot be defeated, only redirected to a new target, and puts the dog down with a bullet to the head. The dog breathes its last as Keys and Julie rush Carruthers away for medical help, leaving the white dog's dead body resting in the sand.