Lucy Bostil, daughter of a Colorado ranch owner, is led by a dog to his master, Lin Slone, who is exhausted from a struggle to capture a wild horse; she revives Lin and they christen the horse "Wildfire." The Bostils have entered Sage King in a race, but Lucy agrees to tame and train the wild horse, since Buckles, her favorite colt, has been stolen. When Joel Creech, a half-witted stable hand, is discharged, he becomes a tool of the Cordtses--who also have entered a horse (Buckles) in the race--in drugging Sage King. Lin and Lucy enter Wildfire under the Bostil colors, and she rides him to victory, When Cordts is disgraced and discovered to be a horse thief, he persuades Joel to abduct Lucy. Joel does so, but first he kills Cordts. Warned by his dog of Lucy's danger, Lin pursues and rescues the girl.