At the close of the Civil War, Lt. Frank Hewitt, a Texan who has joined the U.S. Cavalry, encounters a band of Cheyenne Indians who have illegally left the Sand Creek Reservation on a trading expedition. Because the Indians are unarmed, Frank's detachment merely orders them to return home. After Frank reports the incident to his superior, Col. Chivington, however, Chivington orders an attack on Sand Creek. Worried about Indian reprisals in nearby Texas, which because of the war is occupied mostly by women and children, Frank deserts his post and heads south. Along the way, he witnesses the brutal massacre of the peaceful Cheyenne people at Sand Creek. In Texas, Frank's warnings of potential Indian attacks go unheeded because of the uniform he wears. Even his old flame, Stella Leatham, who has since married, calls him a "damned Yankee." After citizen Dora Hartley is attacked in her home, however, Frank is put in charge of defending the town. He names Hannah Lacey, a tough widow who can shoot, as his sergeant. Aided by the reluctant "Kettle," an Irish-American cowboy, he and Hannah begin to drill the new "soldiers." Among others, the soldiers-in-training include Mrs. Ogden, a haughty dowager from Charleston, her black maid Hetty, dance hall entertainer Lucy Conover, and Ann Martin, to whom Frank is secretly attracted. Although Kettle has convinced the women they must go to a safer location, Frank is certain they will all be killed if they leave and sets the horses free. Frank then catches Kettle trying to steal their one remaining horse and imprisons him. Speaking tenderly from his jail cell to his sweetheart, Mary Wheeler, who is pregnant with his child, Kettle promises to marry her if she will release him. After she does, Kettle shoves her to the ground and escapes to a ranch house some miles away. There he encounters one Mexican and two American outlaws, who force him to reveal the location of the women and their jewels and money. Then Kipper, the outlaws' leader, shoots Kettle, and the bandits ride out to a nearby mission. When the women see them, they raise their rifles and order the men to leave. The outlaws ride into the countryside, encounter a large group of angry Indians and encourage them to attack the mission. The women hide on the roof, and the Indians, assuming the outlaws lied to them, fatally shoot the men. As the band rides away, however, young Bax stands up too soon and is spotted. Though short on ammunition, the women drive their attackers off. Later, Frank devises a plan and commands the women to place gunpowder "bombs" just outside the mission gates. The next morning, as the Indians attack, Sgt. Lacey and her troops fire their rifles at the bombs, causing them to explode and injure the Indians. In the resulting confusion, Frank finds the tribe's retreating medicine man and kills him, then returns to the mission with the corpse. Just as the ammunition runs out, the women hoist up the medicine man's body, causing the Indians to flee. Later, Frank returns to the Cavalry to face desertion charges, but Chivington refuses to believe that the women successfully defended themselves against hostile Indians. During the trial, Sgt. Lacey and her troops demand that Frank be released. The colonel is outraged, but the general states that the wrong man is on trial and arrests Chivington for his role in the Sand Creek massacre. As the women congratulate their former lieutenant, Ann approaches, and Frank embraces his new love.