 Mine owner George Perez, transporting a load of uranium, is ambushed and left for dead after a fall over a cliff. Badly hurt, he makes his way to town doctor Frank Harding (Leo Cleary), secretly the boss of the outlaw gang working with a foreign government to steal the uranium,who poisons him and passes his death off as the result of an accident. The mine passes into the hands of rancher/businessman Craig Bennett, who makes a claim for the Uranium loss and the company sends Roy Rogers (Roy Rogers) to investigate. He comes to Coronado posing as a cowhand looking for work and gets a job as a member of a line crew that includes Foy Willing (Foy Willing) and the Riders of the Purple Sage(Darol Rice, Al Sloey and George Bamby)working for Bennett s Coronado Power and Light Company. Roy also runs into an old friend, Sparrow Biffle (Pat Brady), who is a helper to Bennett s secretary Pam Reynolds (Dale Evans.) Just as Roy has uncovered evidence linking Dr. Harding, henchman Ross (Clifton Young) and his men succeed in hi-jacking the ore from a warehouse and on the trail to where their contact man is to pick it up by airplane and fly it out of the country.