Producer Hal Roach was known for his comic shorts; however, his first foray into the world of features wasn't a comedy, but a Western. Naturally, it wasn't your typical Western -- the star was Rex, the Wonder Horse. Rex is Black, a wild stallion who is the leader of a herd near the Mexican border. Cowboy Billy Blair (Leon Bary) is determined to capture Black, but the horse is too fast and crafty for him. Cowboy and horse ultimately form a common bond during a forest fire as Black is trapped and Blair shows him a way out. Black becomes devoted to Blair. Ranch foreman Wade Galvin (Pat Hartigan) is secretly a horse thief, and he tries to put the blame for his crimes on Blair. With the help of Black, Galvin is rounded up and proven to be the guilty party. Blair wins the love of pretty Mary Fielding (Edna Murphy), and Black is allowed to return to the wild. Hal Roach himself wrote the story to this film.