Bent on unearthing the cynical traitor who sold information to the enemy and caused the death of a dear brother-in-arms, the battle-tested former Union cavalry officer, Colonel Cord McNally, teams up with a pair of ex-Confederates after the Civil War. Now, as honest friends, the three companions ride into Rio Lobo--a dusty town in the middle of the desert overcome by corruption--to bring to justice the one who sold McNally out; however, the town is rife with the betrayer's murderous cut-throats....