A cavalry unit in Colorado is conducting two important cargoes to Fort Reunion, home of the 11th Colorado Volunteers: Cresta Marybelle Lee (Candice Bergen), the fiancée of an officer in the unit until two years ago, when she was taken by the Cheyenne, and who just escaped; and Captain Battles (Dana Elcar), the paymaster, with a strongbox containing gold. The men are tired -- almost asleep in their saddles -- and frustrated, and doubly so by the presence of Cresta, whose beauty and reputation (by virtue of living two years with "savages") is driving them to distraction; all except for Honus Gant (Peter Strauss), a neophyte trooper and wide-eyed innocent. The detachment is ambushed by a Cheyenne war party and the only survivors are Cresta and Honus, who learn to tolerate each other as they struggle across the wilderness and the desert in search of help. An encounter with white trader Isaac Q. Cumber (Donald Pleasence), a profiteer who is running guns to the Indians, nearly results in their deaths, and Honus is seriously wounded.
Cresta goes off in search of help and is picked up by a cavalry scout and brought to the 11th Colorado, whose commanding officer, Col. Iverson (John Anderson), is planning a punitive strike against a peaceful Cheyenne encampment over the massacre of the paymaster's party. Cresta tries to secure help for Honus but Iverson is too busy planning bloodshed, and her fiancé, Lt. McNair (Bob Carraway), is just too eager to pick up where he left off with her to listen to her warnings. She rides out on her own and returns to the village where she'd spent the previous two years, while Honus manages to survive to reach Iverson. He ends up along for the assault on the village, which takes place despite the chieftain Spotted Wolf (Jorge Rivera) flying a flag of truce and an American flag given him at a previous negotiation with the whites. The Native Americans defend themselves when fired upon with artillery and rifles, and all hell breaks lose -- virtually all of the men in the village are killed in the first assault, and then the soldiers spot the women, children, and old men, and there begins an orgy of rape, mutilation, beheadings, dismemberment, and torture before Honus' horrified eyes by joyously shrieking soldiers. Cresta kills a soldier who tries to rape her and intends to die with her Native American family but is pulled out, only to watch the slaughter continue. In the end, Honus is left to be marched back to Fort Reunion as a prisoner for trying to stop the killing, and Iverson expresses pride and satisfaction at what he's done, while Cresta and a tiny handful of survivors -- almost all old men and women -- watch in mute horror and anger.
