Texas Ranger Jake Cutter arrests gambler Paul Regret, but soon finds himself teamed with his prisoner in an undercover effort to defeat a band of renegade arms merchants and thieves known as Comancheros.

In 1843 Texas Ranger Jake Cutter arrests gambler Paul Regret in Galveston and heads for Louisiana. There Paul is wanted for killing a man in a pistol duel. En route, Paul catches Jake off guard, clouts him with a shovel, and makes his escape. Jake returns to Ranger headquarters and is ordered to impersonate a gun smuggler in order to ferret out the secret stronghold of the Comancheros, a band of white renegades selling liquor and guns to the marauding Comanches. While stopping off at a small town, Jake again runs into Paul and again takes him into custody. After helping some ranchers ward off an Indian attack, the two men reach the Comancheros' hideout, where Paul encounters Pilar, an adventuress he knew and loved in Galveston. Aware that Jake is a Ranger, Pilar decides to join him and Paul in their fight against her father, Graile, the Comanchero leader. Early one morning, they sneak out of the stronghold and set fire to the gun powder magazines. Before they can reach safety, however, they are attacked by bloodthirsty Comanches, but the Rangers ride to the rescue and repulse the attack. After saying goodbye to Pilar and Paul, Jake rides off into the sunset.