In 1882, after Apache Indians terrorize innocent townspeople, Captain Jeff Packard of the U.S. Army, whose mother and father were killed by Apaches, is assigned to kill Apache warrior Geronimo. Packard takes the name "Jeff Smith," and travels to the town of Larksberg to meet his contacts, Frank Cochran and Fletcher. At the local gunsmith's shop, Packard poses as The Waco Kid, fooling outlaw Walt Anderson and his henchman, Jennings. Later, when he sees Luke, another Anderson henchman, attack a young woman named Julie Scott, Packard shoots him in the hand. Meanwhile, Major Clem French, concerned about Indian attacks, orders a military escort for a stagecoach carrying payroll funds. When Red, one of Anderson's gang, learns that The Waco Kid is actually in the penitentiary, he and Frank, who is also working secretly for Anderson, become suspicious of Packard. At the saloon, meanwhile, Packard asks Frank and Fletcher to intercept a shipment of guns at Fort Broken Bow so they will not fall into Geronimo's hands. Later, Fletcher takes Packard to a shack outside of town, and there they discover Frank's slain corpse. Red then kills Fletcher and escapes. The cavalry chases Anderson's men to the ranch owned by Julie's father Jason, and the outlaws take Jason hostage, placing him inside one of the wagons containing the guns. The cavalry stops to check the wagons for the guns, but are called away by Apache smoke signals before Jason or the guns are discovered. After Packard writes his name on a grave marker, the gang suspects that he is working for Army intelligence. Later, Packard creates a diversion to give Julie a chance to escape, but she is apprehended by Luke. The cavalry catches up to Packard and the gang, confiscates the guns and arrests them. Inside the jail at cavalry headquarters, Packard maintains his cover. To confuse Geronimo and his men, the cavalry moves the guns to another wagon, which is to be sent from Fort Broken Bow to Fort Apache. Later, Packard recommends that the cavalry arrange for Anderson to escape so they can follow him to Geronimo. Once free, Anderson tells Geronimo what has happened, while Packard warns the major that the fort will be attacked unless they surrender the guns to Geronimo. While Anderson learns Packard's true identity, the major helps Julie and the major's wife Martha to board a stagecoach leaving the fort. After Packard tells him that the major wishes to negotiate at the fort, Geronimo demands three wagons full of guns in exchange for peace. When the major refuses, the Apaches attack. Later, Packard leaves the fort to warn the stagecoach not to continue. After Geronimo learns that the guns have been removed, he and his men kill the major. Geronimo then goes to Fort Apache to locate the guns, but when he realizes that they lack firing pins and are therefore useless, he kills Anderson. Packard reaches the stagecoach, but the Indians attack, and Martha is killed. After Packard grabs Geronimo's knife and stabs him in the back, he and Julie embrace.