Rex the wonder horse's owner is murdered by Joe Regan, the leader of a band of smugglers. RCMP Sgt. Jack Gordon has been sent to capture the villain. Rex vows vengeance on Regan and helps Gordon capture him.

Chasing the man who had caused the death of his sister, Jack Walsh rescues Mary Winters from the unwanted attentions of a drunk, and learns that she has been lured to Mexico by the false promises of an ex-prizefighter "Kayo" Mooney. The latter kidnaps Mary but Jack wins the showdown and Mary, and finds that Mooney is the man he was looking for.

It's time for the stagecoach race to win the mail contract and the only entries are Reden and Farrell. Reden's men kidnap Farrell's daughter and then force him to withdraw. Wally rescues Ruth, buys out Farrel, and enters the race himself. But Reden has his men planted along the course to make sure Wally doesn't win.

During a rescue of Mary and her father, Bob Bartlett finds a good horse, which later causes him to be mistaken for Butch Coleson, a wanted outlaw. Wounded by a posse, Bob heads for Poker Flats hoping to capture Coleson for the reward.

Horses are being stolen by a white stallion known as "The Phantom of the Desert." A cowboy sets out to find who's behind it.

A gang of bank robbers holes up at a cowboy's ranch. One of the robbers turns out to be his brother. After the brother is killed by the gang, the cowboy tracks them across the desert.

It seems that an evil saloon owner not only wants this valuable steed for himself, but also its owner, the beautiful Mary Ellis. Enter honest gambler Jack Crosby, who wants to settle the score.

A forest ranger comes to the aid of his fiance and her father when a crooked rancher and his gang try to force them off their land.

Human cowboy hero is teamed with Rex, King of Wild Horses, an ornery critter but a magnificent animal.

Jed Campbell, a "skypilot," and Nanette, a dance hall girl, meet when each goes to rescue Rex, "King of the Wild Horses," from a trap.