An English aristocrat is taken prisoner by a tribe of American Sioux Indians and given to the chief's aging mother as a servant. Gradually, he embraces the tribe's way of life and falls in love with the chief's sister. The constant threat of ambush by a rival tribe and rigors of survival now fill the days of this man called "Horse." He is eventually given a chance to prove his worthiness and be accepted into the tribe. But in order to be accepted with honor as an equal within the tribe, he must endure the Sun Vow.