Maj. Howell Brady of the U.S. Cavalry is sent to Fort Clark, Texas, with his two sergeants, Luke Schermerhorn and Augustus Wilks, to put down bloody raids on settlers by Kiowa Indians. Brady's arrival is greeted with little enthusiasm by Col. Jackson Meade, the commanding officer at Fort Clark, who sees Brady's presence as a threat to his authority. Meade balks at Brady's plan to use the peaceful Seminole Indians to keep the Kiowas at bay, but Brady goes ahead with his plan and meets with Maygro, chief of the Seminoles. Maygro initially resists Brady's plan, but later changes his mind after seeing the ease with which Brady and his men fight off raiding Kiowas using their high-powered Henry repeating rifles. In exchange for Maygro's help in stopping Kiowa raids, Brady gives him $500, food and a promise that the Seminoles will be given the fertile Santa Media Valley. Brady's decision to quarter the Seminoles at Fort Clark is met with resistance by Meade and many others, and he soon finds that his only ally at the fort is Elaine Corwin, a widow whose husband was killed on a scouting mission. Brady and Elaine soon fall in love, and Avis, Maygro's daughter, becomes jealous of the romance. The training of the Seminoles proves a success, and they repel the Kiowa raids. During one of the attacks, Brady sees a white man flee with the Indians. Although he is unable to get a good look at the man, Brady finds the sword he dropped, which bears the name "R. G. Corwin." Later, while questioning Elaine about her husband, Brady learns that he was only presumed dead, and that he was associated with a Mexican group determined to incite the Kiowas to battle. Brady nearly loses his Seminole support when Meade fails to deliver a food supply promised to the Seminoles. Maygro leads his tribesmen out of the fort, but Brady manages to win them back after stealing the food and delivering it himself. Meade jails Brady and his sergeants for the theft, but they are freed by Elaine and some of the Seminoles. Soon after the jailbreak, Brady discovers that the Kiowas are preparing a massive assault on the fort, and he returns to warn Meade. Meade disregards the warning and is about to return the men to jail when one of his own patrols arrives with the same news. A fierce battle ensues between the Kiowas and those inside the fort, but Brady outwits the attackers by sneaking out of the fort and firing on the Kiowas from behind. Among the many killed at the fort is Corwin, who revealed himself to be a traitor by fighting on the side of the Kiowas. Having saved the fort from destruction, Brady looks forward to his next mission with Elaine at his side.