As the Civil War rages on, a weary Confederate officer leads his men across the Rio Grande in search of firearms to continue the fight. What begins as a military mission soon becomes far more complicated when they are drawn into a dangerous Mexican uprising filled with shifting alliances, political unrest, and competing ambitions. Meanwhile, a persistent Union officer is determined to stop the operation before it succeeds.

Joel McCrea brings his trademark quiet resolve to the role of Major Clete Mattson, while Yvonne De Carlo adds both charm and intrigue as Carmelita Carias. Opposite them, Pedro Armendariz delivers a memorable performance as the ruthless General Calleja, helping fuel a story packed with action, adventure, and borderland intrigue.