Short summary: a love story between a man and two horses. Special features include bisexual bestiality! If you're not into it, don't watch the movie.
The plot is kind of like this: the man and the male horse get captured, then they escape; the male horse meets the female horse, he loves her and is jealous of the man who engages in foreplay with the female horse; later, the male horse flirts with the man, attempts to save the female horse, and destroys two locomotives and causes an explosion that burns quite a few acres of the forest. But he does hook up with the female horse, and in the end the Native American man loses both his boyfriend and his girlfriend.
This movie seriously deserves to be on MST3K. Otherwise, avoid watching it at all times.