Working undercover, Allen and sidekick Mendoza are out to stop the mail train robberies. Rivers and his gang are the culprits and by joining up with them, they hope to get the evidence they need.

Cholita, after a long absence in Mexico City, is returning home to take up her duties as head of the rancho and, as everyone expects, to marry her childhood sweetheart José. Expectations are somewhat dashed as she shows up with Fernando to whom she is engaged. This makes José and Cholita's uncle more than a little bit put out as Fernando is not only not a Mexican, he is also a city slicker afraid of the country.

Tom Kenyon and his sidekick Pierre La Farge are hired by rancher Mike O'Day who, with his daughters Toni and Sugar, provides wild horses for the government remount station.