A cavalry unit located on the Mexican border must control Indian uprisings.

Some time after the Civil War, at a U.S. Cavalry fort near the Rio Grande River, soldiers and their prisoners return after a battle againstthe Apache. The Indians have been leading raids from the Mexican side of the border where the troopers are forbidden to follow. Upon his return to the fort, Col. Kirby Yorke learns that his son Jefferson, whom he has not seen for fifteen years, has been dropped from West Point after failing mathematics. Shortly after, Yorke, a no-nonsense career soldier, gives a new batch of recruits a harsh speech about the difficulties facing them, and then discovers that Jeff is among them. Privately, he later warns his son not to expect special treatment because of their kinship. Far from wanting favoritism from his father, Jeff pushes himself to prove that he can be a good soldier, despite his failure at West Point. During a riding lesson, a U.S. deputy marshal arrives in search of Trooper Travis Tyree, a Southerner who has been accused of manslaughter, but the other recruits keep him hidden. Later, Jeff starts a fight with recruit Heinze, who has insulted Yorke and called Yorke's old friend Sgt. Maj. Tim Quincannon, a "chowder-headed Mick." Quincannon stops the fight, but when he learns the reason for their dispute, instructs them to return that evening to settle their disagreement. This time, the fight is interrupted by Yorke, who demands an explanation. Both Heinze and Jeff refuse to answer, and then apologize and shake hands. One day, Yorke's estranged southern wife Kathleen arrives at the fort and tries to buy her son's discharge from the army. Yorke refuses to sign the necessary release, stating that he will not interfere with Jeff's decision. Both Yorke and Kathleen are still strongly attracted to each other, although neither will admit it, and Yorke leaves Kathleen to spend the night alone. Quincannon then escorts Kathleen to Jeff's tent. When he learns why she has come, Jeff, as his father anticipated, refuses to leave. That night, Apaches attack the fort and rescue the soldiers' prisoners. Yorke leads his men as they go after the fugitives, and while he is gone, Tyree is arrested. Kathleen objects, believing that "Yankee justice" has falsely accused the nice young southerner. Later, Quincannon reveals that fifteen years ago, during the Civil War, Gen. Sheridan ordered Yorke to burn down the plantation operated by Kathleen's family and that is why she left him and prevented him from seeing his son. Meanwhile, Yorke's men meet with some Mexican soldiers in the middle of the Rio Grande. Yorke suggests that they disregard the orders of their governments and work together to catch the renegade Apaches but cannot persuade the Mexican lieutenant. Back in camp, Kathleen is waiting for Yorke's return. They embrace and, after Yorke apologizes, they discuss their marriage. She again pushes for their son's release, but Yorke maintains that Jeff must learn to honor his word. That night at dinner with Sheridan, Kathleen toasts her only rival, the U.S. Cavalry. At the infirmary, where he is incarcerated, Tyree admits that a dispute over his sister led to a violent encounter with a Yankee, but insists that he did not kill him. Soon after, Tyree escapes on Yorke's horse. Expecting more Indian attacks, Yorke evacuates the women and children to Fort Bliss, assigning Jeff to be one of the escorts. Although she realizes that Jeff will be unhappy that he will not be among the soldiers, Kathleen is grateful. The evacuation begins, but soon the small group is under Apache fire, and Jeff is ordered to carry news of the attack to Yorke. By the time Yorke and Dr. Wilkins arrive, the Indians have captured the fort's children. When Tyree, who has been hiding nearby, approaches the regiment, Yorke orders him arrested, but Tyree reports that he has scouted the Apache camp in a village on the Mexican side of the river, where the children are being held in a church. He offers to try to rescue them with two men of his choice. Yorke is worried when one of the chosen is Jeff, but allows them to proceed. While the three men sneak into the church, Yorke leads the regiment across the Rio Grande. Once the children are organized, one of the girls rings the church bell to summon the soldiers. During the ensuing battle, Yorke is shot in the chest with an arrow. On Yorke's orders, Jeff removes the arrow from his father's chest and and helps him onto his horse for the ride back to the fort. Kathleen is waiting, and holding Yorke's hand, accompanies her husband to the infirmary. Later, under Yorke's proud gaze, Jeff receives a commendation for bravery. In the middle of the ceremony, Tyree steals Sheridan's horse and escapes from the deputy marshal with Yorke's encouragement. The regiment then marches off to the strains of "Dixie," played in Kathleen's honor.