In the summer of 1881, a young woman named Lucy Dabney and her father, Maj. Dabney, are found dead in their quarters at Fort Linton in the Arizona Territory. Lt. Tom Cantrell arrives at the U.S. Army's southwestern headquarters to defend the accused, a black sergeant named Braxton Rutledge, who served bravely under Cantrell in the all-black Ninth Cavalry for over six years. Because Lucy was raped and beaten before her brutal strangulation, the case attracts a group of spectators, who harass Rutledge as he is led into the courtroom. Presiding over the court-martial is Col. Otis Thornton Fosgate. After Fosgate ejects the onlookers from the room, angering his fluttery wife Cordelia, prosecutor Capt. Shattuck questions a series of witnesses, who describe the events that occurred on the day of the murders. Mary Beecher relates how she returned to Arizona on that day after an absence of twelve years. Because her father failed to meet her at the train station, she found herself alone. Upon discovering the station master's lifeless body, she became utterly terrified. Rutledge then suddenly appeared and defended her from two attacking Indians who, along with a larger group of Mescaleros, had broken out of the San Rosario Reservation earlier in the day. Cordelia then tells the court that she saw Rutledge tumble from Dabney's quarters after hearing two shots fired. Earlier in the day, Cordelia had told Lucy that even though Rutledge had been the girl's friend and riding instructor for years, it was unseemly for her to speak with him. As the fort doctor and then Tom himself take the witness stand, the court learns that Rutledge, arriving at Dabney's to warn the major of the Apache breakout, found Lucy's body, but was forced to shoot the major in self-defense when Dabney, entering the room, wildly fired on him. Convinced that no one would believe a black man's story, Rutledge then fled in a panic to the train station, where he aided Mary. Tom, leading a detachment of Ninth Cavalry soldiers, followed and arrested Rutledge, then proceeded toward the Beecher ranch in pursuit of the Apaches. On the way, they discovered the body of young Chris Hubble, who had been killed by an Apache lance. During a subsequent skirmish with the Apaches, Rutledge escaped, but as he approached the Beecher ranch, he realized that the patrol was riding into an Apache ambush. After warning the soldiers, he commanded them during the battle, only to be taken back into custody afterward. Following Rutledge's testimony, Shattuck declares that the sergeant's heroic actions were intended merely to earn him the court's mercy, whereupon Rutledge protests that the Ninth Cavalry is his home and the source of his self-respect. Next, Mary testifies that after the battle, Tom found young Lucy's gold cross as well as a jacket marked "CH" on the body of a dead Apache. Tom presents these items as evidence that Chris was the murderer. Shattuck angrily accuses Tom of attempting to pin the crime on a dead white boy merely to salvage the life of a black. Chandler Hubble, Chris's father, then admits under oath that his deceased son committed the crimes. Realizing that the jacket was too large for young Chris, Tom accuses the elder Hubble of the murders, whereupon Hubble confesses. Following Rutledge's acquittal, Mary and Tom are united, and the sergeant again leads his proud soldiers.