In the 19th-century American West, a young Kiger Mustang colt, Spirit, is born to a herd of horses. Spirit soon grows into a stallion and assumes the role of leader of the herd, whose duty is to keep the herd safe. Spirit is a courageous leader but has great curiosity. Spotting a strange light one night not far from his herd, the stallion is intrigued and investigates. He finds restrained, docile horses and their human wranglers sleeping around a campfire. They wake up, and seeing him as a magnificent specimen, chase and capture him, taking him to a US cavalry post.