Patrick Angus O'Toole is a military officer assigned to investigate a gang of gunrunners operating near Fort Sumner in the Dakota Bad Lands. At the fort, O'Toole comes to the aid of Mary Owen, who is being harassed by Captain Blake. The irate Blake gives Mary's cowardly brother, Hal, 24 hours to pay his gambling debt. In desperation, Hal robs the Pony Express, a crime for which O'Toole is arrested.