The gold mine belonging to "Gun" Barlow (Edward Keane) is worked out, and Barlow attempts to buy adjacent land, with the hopes his gold vein will continue, from town postmistress Marion Saunders (Rosalind Keith) who, keeping a vow she made to her father on his death-bed, refuses. Marion also owns the local stage line, and Barlow, "Bull" Feeney (Al Bridge) and Steve Hickman (Ben Welden) hatch a plot to have mysterious accidents happen to the mail coach, hoping that Marion will give up and sell out. They hire two henchmen, Slim (George Chesebro) and Shorty (Art Mix) , to do the dirty work and they wreck the coach by causing a huge rock-slide, and stage-driver Andy (Arthur Stone0 is hurt and left to die. A mule skinner named Jim Bradley (Charles Starrett) comes along, picks up Andy and the mail and heads for town, where he tells Marion his name is "Skinner" and offers to run the mail while Andy is recovering. Barlow and Bull drop by and rag him about his mules, and they force a bet that their horses can beat his mule-team in a race. If he loses, "Skinner" will be put to work in Barlow's mine. He wants to get into the mine so he can look things over, as part of his job as a postal-inspector working undercover. Complications arise but none that Jim Bradley can't handle.