In Missouri during the final days of the Civil War, brothers Frank (Wendell Corey) and Jesse James (Macdonald Carey) engage in a skirmish with Union soldiers, killing one before fleeing. After the war's end, amnesty is declared, but the brothers are betrayed by Union officer Maj. Trowbridge (Ward Bond), whose brother they killed. Along with the Younger brothers, Frank and Jesse turn to robbing banks, while Trowbridge, still bent on revenge, opens a detective agency to find and stop the brothers.