In 1876, a U.S. Cavalry troop under the command of Capt. Storm prepares to evacuate white settlers from the Buffalo Valley region in the Southwest in advance of a possible Comanche and Kiowa Indian attack. Once enemies, the Comanche and Kiowa tribes have ended their feud and are now banded together to fight the injustices of the "white man." Hoping to avert bloodshed, Storm meets with Indian chiefs Growling Bear and Black Eagle, but the "powwow" turns violent when Growling Bear's son, Running Deer, engages the captain in a knife fight to defend his father's honor. Storm quickly subdues the young Comanche, and then secures a promise from Growling Bear to hold off his planned attack for two more days. Storm believes that two days is sufficient time to evacuate the area of settlers if negotiations between the Indians and a soon-to-arrive U.S. Government emissary end in failure. With the help of "Injun," a white scout reared by Sioux Indians, Storm and his cavalrymen begin gathering the settlers of Buffalo Valley for the treacherous journey to safety across Thunder Pass. Among those being escorted out of the valley are Tulsa, a prospector; Charity, a pretty young woman who falls in love with Corporal Riga; Murdock, an embittered and rebellious woman whose father was killed in a previous Indian massacre; a seriously wounded man named Dalstead; and Bergstrom, a mysterious St. Louis skin trader. Soon after leaving Buffalo Valley, Bergstrom secretly signals some Indians who are trailing the caravan to attack the gun wagon and steal the horses. The situation for evacuees grows worse when it is discovered that their water supply has been salted. Some members of the caravan protest Storm's decision to carry the unconscious Dalstead across the pass, insisting that it will cause the caravan to slow down. Storm, however, begins to distrust Bergstrom's motives, and suspects that Dalstead may be the government emissary sent to negotiate the peace treaty. As the caravan approaches Thunder Pass, Bergstrom leads some of the others in a rebellion against Storm, challenging his leadership and his decision to take Dalstead along at all costs. Bergstrom's attempt to take over command of the caravan ends in failure when Storm, the only one who knows the way to safety, refuses to guide the group if Dalstead is left to die. When the caravan finally reaches the pass, only a hostile Indian war party is waiting for them. A fierce gun battle ensues, during which Dalstead regains consciousness long enough to tell Storm that he is, indeed, the government agent, and that the food shipment for which the Indians are waiting has been sent to Fort Terahawk. Bergstrom is exposed as the actual gunrunner and a traitor when he is caught trying to shoot Dalstead, and Tulsa shoots and kills Bergstrom as he tries to flee. Shortly afterward, Growling Bear arrives and orders a halt to the Indian attack. With Storm's reassurance that the food shipment will be at Fort Terahawk, Growling Bear offers the caravan a guarantee of safe passage to the fort. Nearing the end of the journey, Storm looks forward to his next assignment and insists that Murdock accompany him.
