Holly Nelson returns to Williams, Arizona to reunite for the summer with her beloved mustang, Bartholomew, and finds the boy she had challenged last year to a horse race asking for her help. Someone has stolen his father's cattle. Holly agrees to help as do her best friend and stepbrother, but nothing has prepared her for being chased by cattle thieves and getting lost in the wilderness. Fortunately, a Hopi friend is with her as a guide, and the mustang paint they come to share becomes Holly's only hope for trying to stop the thieves from destroying the entire herd of cattle.