Four bandits swoop down on a California bank and flee with $98,000, leaving a truck as the only clue to their identity. Jane Hartman, bank secretary, recognizes the truck as one on which her brother Charles worked. Fleeing to her brother, she is trapped by the gang, composed of its master-mind, Gibbs, Sidney, a gunman, and Randall, a blackballed airplane pilot. Under threat of bodily harm to her brother, she lures truck-driver Tony Andrews to the hideout, and he is forced to help them in their escape attempt.

It is California in 1852 that only recently being surrendered by Mexico to the United States and admitted into the union. Most of the land-owners of California were the descendants of the Dons who had colonized it a hundred years before and whose title deeds bore the signature and seal of a long-dead Spanish king. But, by a loop-hole in the law, the title-deeds of the Dons could not be recognized, and this opened the door of organized gangs of land-grabbers, such as the one led by Joe Kincaid, to operate with a prime excuse for legitimate plunder and robbery. In most cases the law was unable to cope with the situation. Then Rosita Castro, the daughter of Don Pasqual Castro, masked and disguised as a man, organized a band of vigilantes to fight against the tyranny of the outlaws, aided by an undercover federal agent, Jim Kearney.