John Wayne stars as Lt. Col. Kirby Yorke, whose devotion to duty has cost him his marriage to his beloved Kathleen (Maureen O'Hara). Yorke gets word that his son, Jeff (Claude Jarman Jr.) -- whom he hasn't seen in 15 years -- has been dropped as a cadet from West Point, and that he lied about his age to enlist in the cavalry, in an effort to redeem himself. By chance, the boy is then assigned to his father's post. Once more, as a function of his duty as a cavalry officer, Yorke must sacrifice his love of family -- he cannot show any preferential treatment to the boy, or exhibit any sign of love and affection. But Jeff is too strong to be injured by his father's actions, and already enough of a man that he is befriended by two older recruits, troopers Tyree (Ben Johnson) and Boone (Harry Carey Jr.), who watch out for him while taking him in as a virtual equal. Yorke's resolve is further tested when his estranged wife, Kathleen, arrives at the post, the better to look after her son -- and possibly to buy back the boy's enlistment, which Yorke, as commanding officer in a remote post with a critical shortage of men, can't and won't permit. After an attack by the Apaches, Yorke orders the post's women and children to be moved to safety, and Jeff is assigned as part of the troop conducting the caravan, despite his wish to participate in the planned action against the Apaches. The caravan is attacked, and the wagon with the children is taken by the Apaches to their encampment in a deserted village across the Rio Grande in Mexico. Yorke has been given permission by General Sheridan (J. Carrol Naish) to take his men into Mexico in pursuit of the Apaches, but the punitive expedition is now a rescue mission, as the Indians' night-time vengeance dance is the prelude to certain slaughter of the children at daybreak. As part of the mission, it's up to Tyree, the slyest man in the troop, to infiltrate the enemy camp, and he chooses Jeff and Boone as the two men he wants with him on this dangerous mission.