Part of a trilogy about the US Cavalry after the Civil War, this features the Apache wars, with Lt. Col. Kirby Yorke (John Wayne) in a remote post on the Rio Grande training raw troops to fight the Apaches, one of whom is his own son, Trooper Jeff Yorke (Claude Jarman Jr.). He’s been apart from the young man since he parted with his mother Kathleen (Maureen O’Hara) years before. Yorke is extra strict with Jeff to prevent seeming to display favoritism and their relationship is strained. The boy’s mother (and his estranged wife) arrives to try to keep her son safe, and the old romance between her and Yorke comes back to life as they struggle with what is best for their son. General Sheridan (J. Carrol Naish) arrives with a dangerous assignment for Yorke, an incursion across the Mexican border to attack the Apaches. Yorke could be court-martialed or cause an international incident whether he succeeds or fails, and his troops are too few and very green. He also has to weigh his obligations to his son and wife with the demands of his military service in choosing how to proceed.