As the traveling Roy Rogers Western Show passes the ranch of ex-showman Col. Harkrider, a sudden storm forces them to take refuge at the ranch. The next morning, Harkrider's grandson Larry becomes frightened when he sees the show horses. Larry is asked to lead the offspring of Roy's horse Trigger, whom they call Junior, to the stable, and allows the horse to wander off. After Roy and his press agent, Splinters, realize that Junior is missing, they search for him and find that Monty Manson of the Range Patrol, which is supposed to protect the ranchers' livestock from harm, has taken the horse into custody. Roy retrieves the horse and returns to the Harkrider Ranch with Splinters. There, Col. Harkrider and his daughter Kay decide to visit an army remount station, Fort Dalton, which is auctioning off its horses. Roy and Splinters accompany them to the auction, where Kay persuades her father to buy a horse. Meanwhile, at the remount station's isolation barn, Manson examines a white stallion slated for destruction because of its killer instincts. When Roy and Splinters notice the horse, they discuss purchasing it for the show, but then are attacked suddenly by Manson's men. Roy and Splinters fight them off and rush to purchase the horse, but discover that the auction has just closed. After the crowd disperses, Mason bribes a veterinarian named Doc Brown into letting him have the horse. That evening, the Range Patrol releases the wild stallion, which kills some of the ranchers' horses. When they learn that a phantom white horse is to blame, the ranchers vote to continue their support of the Patrol. The next evening, as the family celebrates Larry's tenth birthday, the phantom animal attacks Roy's horses in the stables. Trigger fights the phantom, but is knocked unconscious when the wild stallion kicks him in the head. The phantom kills Harkrider's new horse and disappears into the night. Later, Doc determines that Trigger has been blinded by a severe blow to his optic nerve. After Doc learns that the stallion has killed some of the ranchers' horses, he threatens to reveal the scheme, but Manson shoots him. After Roy and Splinters spot the stallion near the ranch, they are ambushed by Manson's men, and Splinter's horse returns to the ranch without its rider. Kay and the ranch hands form a search party, leaving Col. Harkrider alone at the ranch. The stallion returns to the ranch and attacks the Col., knocking him out of his wheelchair and again kicking Trigger. The blow releases the pressure on Trigger's optic nerve and restores his sight. As the phantom horse prepares to kill Junior, Larry, who has overcome his fear, returns to mount Junior and follows the search party. When he catches up to them, he explains what has happened, and Kay decides to return to help her father, while Larry leads the party forward. Meanwhile, Roy and Splinters hide behind a large boulder as Manson's men fire on them. When the wild horse attacks Manson, Roy shoots and kills the animal. The next day, as the show prepares to depart for its next venue, Roy and Splinters say goodbye to the Harkrider Ranch.
