The owner of the Bar-M Ranch in New Mexico is detained by business in Chicago, and sends his daughter, Bertha Murdock, with her chaperone, Mrs. Fairchild, to take charge of the ranch. This upsets the ranch foreman, Frank Lawson, who has had pretty much of a free hand during the owner's absence. Upon her arrival, he rides to the town of Cerro Gordon and meets with several rough-looking characters. Later, a stranger, George Barton, with his Police Dog, Arno, is riding through the hills and observes Lawson and some men in suspicious activity but, before he can ascertain what it is, Lawson spies him and fires some shots in his direction. Barton meets Bertha and she hires him as a ranch-hand over Lawson's objections. The townspeople are disturbed by the threat of Federal Officers taking over the district, unless a band of smugglers who have been operating on both sides of the border are stopped. THe smugglers are led by Lawson who fears that one of the gang-members, Slim, is a weakling that might tip-off the Sherill, 'Wild Bill,' about their activities and, also wanting to get rid of Barton, he murders Slim and pins the blame on Barton. Bertha witnessed the killing and Lawson has his men take her to the gang's hideout. Arno follows them. The sheriff and his posse arrive at the ranch just as Barton is riding away to rescue Bertha.
