Father killed, fiancé wounded, gold stolen, Ruth Masters is distraught over what's been happening to her Arizona stagecoach line and considers leaving the business for good. Saloon owner Steve Taggert is pleased, hoping to increase his holdings in Mesa City with her gone.
A retired marshal, Buck Roberts, rides into town, selling cattle. In the saloon he and the others encounter Colonel Tim McCall, a preacher who objects to Sunday sales of whiskey. Buck offers to assist Ruth by driving the stage carrying the next gold shipment, with her recovering sweetheart Joe going along to keep an eye on things for her. A cattleman, Sandy Hopkins, also volunteers to help.
The stage is robbed by masked men. Gold is found in Buck's saddlebags, so he is arrested and some of the townspeople demand that he be hanged. Joe reveals that Buck, anticipating the holdup, hid the gold safely while the robbers got away with nothing but worthless rocks. Buck, Tim and Sandy all turn out to be ex-lawmen, now working undercover to expose the criminals in town. They ride off their separate ways, their work here done.
