In the late 19th-century American West, a Kiger mustang colt, Spirit, is born to a herd of wild horses; he grows into a stallion, and assumes the leadership of the herd. One night, upon following a strange light near his herd, Spirit finds horses tied to a log and their wranglers sleeping around a campfire. The men awaken, and, after a chase, capture Spirit and take him to a US cavalry fort.