In an ingenious scheme, Gridley is mining silver from an old Mexican mine, and sneaking it across the border via an underground passage that links to his own worthless mine. Roy is a vigilant border guard who investigates and finds the secret passage to the Mexican mine. When he sends gal pal Lee Madison for help, she is captured by the unscrupulous Gridley. Roy sends his horse trigger for help and Gridley's gang is captured. Now it's up to Roy to come to Lee's rescue.