The mustang stallion Spirit grows up to proudly succeed his father as leader of the Cimarron herd in the unspoiled Wild West. When 'civilization' reaches Dakota territory, naive curiosity gets him caught by cowboys and sold to the US Cavalry. Its method of training by breaking a horse fails utterly on him. Just when the colonel intends to shoot Spirit, the equally indomitable captured young Lakota brave, Little Creek, escapes on his back. He also tricks him to a coral with his beloved mare, but shows respect and wins some trust. As the railroad arrives, the Indian village is wrecked and Spirit gets captured for use as a draft-horse. When the stallion realizes this project threatens his whole world, he escapes and unleashes the fury of a force of nature, ultimately teaming up with Little Creek.