South of Sonora

Bill Tracy, a Cattleman's Protective Association agent, working undercover, on his way to Sonora, a town dominated by rustlers, saves Betty Carter from a situation, but her rancher father---believing Blackie's suggestion that Bill is a rustler---forbids her to see him. Bill and his pal, Heinie Schmaltz, rescue each other from various plots and ambushes by the rustler, and eventually discover that Blackie, Carter's foreman, is the leader of the rustlers.