Hopalong Cassidy (William Boyd) tries to help a young woman protect her mine from ore-stealing outlaws. Gwen Gaze, George "Gabby" Hayes, Russell Hayden, Paul Sutton.
Hoppy goes after some outlaw miners who have been stealing ore from heroine Gaze's mine. In order to catch the villains in the act, Boyd must spend much of the movie crawling around in dark mine shafts, making it kind of hard to enjoy the wide expanse of western scenery.