Thunder, a dog raised by Ellen, a sheepherder's daughter, is driven to the wilderness by the brutal treatment of her father, Bill Garside, and becomes an outlaw; when grown, he takes command of a wolfdog pack. Later, Ellen, driven from her home by the same brutal herder, seeks refuge at the cabin of Neal Barrett, the forest ranger; she is pursued by the hungry pack and is stranded on a rocky cliff where Thunder once again encounters his former mistress. He challenges the pack in her defense, provoking a battle between himself and a rival for his command. Later, Thunder rescues Ellen from her brutal father.