In one of his first westerns, Johnny Mack Brown plays Kirby Tornell, who does the "Robin Hood" bit on the wide open spaces. When not flummoxing the Cavalry, Kirby relaxes by playing the piano and rendering a song or two. Despite Kirby's notorious reputation, Carol Winfield (Evalyn Knapp), the daughter of the hero's perennial foe General Winfield (George Irving), can't help falling in love with him. And in the end, Carol surrenders totally to Kirby, riding off with him into the sunset. A strong cast of silent-film veterans (ZaSu Pitts, J. Farrell McDonald, Raymond Hatton) helps lift Vanishing Frontier well above the norm.