At night, Lightning the dog and his mate howl to one another, and Lightning leaves the side of his sleeping master, Jed Strom. The next morning, John, Jed's abusive father, blames Lightning for the death of a piglet. Later, school lets out for summer vacation, and Jed and Lightning become heroes after they rescue Jed's teacher, Miss Wilson, from an abandoned mine shaft where she was chased by a bear. When fall begins and school is back in session, Lightning goes to visit his mate and their puppies. As Jed and Lightning walk home from school one day, a bear attacks Lightning's family, and his mate is killed while protecting the pups. Jed rescues the puppies and puts them in the barn, but John finds them and places them in a bag, which he then throws in the lake. Lightning manages to save the puppies from drowning, but in the meantime, Jed, after finding the puppies gone, begins to weep and John prepares to give him a beating. Lightning growls threateningly at John, causing him to fire his shotgun at the dog, but Lightning escapes. While John sets bear traps throughout the forest to kill Lightning, Jed builds a house in the woods for the dogs, and his mother tries to console him. Later, when a bear attacks a piglet, Lightning saves it, but John still believes Lightning to be a menace. While chasing Lightning through the woods with his shotgun, John is caught in one of his own traps and mauled by a bear, but Lightning comes to the rescue just in time and fights the bear until John can shoot it. Jed suddenly arrives, and believing Lightning to be dead, points the shotgun at his father; however, Lightning quickly regains consciousness. John realizes the error of his ways and finally believes that a dog truly is man's best friend.