Based on a Zane Grey story, The Last Trail stars virile cowboy hero George O'Brien in a largely anti-heroic role. Escaping from a posse, the "good bad man" (O'Brien) boards an Eastbound train, where he strikes up a friendship with a genial gangster (J. Carroll Naish). Later on, the cowboy returns to the West as a member of the gangster's gang. He poses as the heir to a vast cattle ranch, never dreaming that he really is the heir. When the truth is revealed, the wayward cowboy switches to the side of the Law, while another of the gangster's flunkeys (Claire Trevor) reveals herself to be an honest newspaperwoman -- and thus a suitable candidate for romance.