In Jun 1876, at Fort Abraham Lincoln in the Montana Territory, Celie Donlin, the neglected wife of Capt. Phillip Donlin of the U.S. Cavalry, tries to convince her lover, Lt. John Haywood, to resign his commission and leave the Army with her. Unknown to them, Phil has returned early from his patrol and has heard everything. The unrepentant Celie tells Phil that she no longer loves him and the heartbroken captain leaves the next morning on another patrol. After three weeks, Phil tells his exhausted men that they must keep up their grueling pace in order to arrive at Camp Yellowstone and warn Gen. George Armstrong Custer of the large buildup of Sioux Indians before he leads the Seventh Cavalry to the Little Big Horn River. While resting at a water hole, Phil's unit is joined by John and his unit, who have been sent to recall Phil to Fort Lincoln. Told that Custer has already left for Little Big Horn, Phil decides to disregard his orders and attempt to warn the general. John argues that such a mission would be suicide and refuses to subject his men to such a hazard, so Phil lets John's detail return to the fort, but orders the lieutenant to join his patrol as second-in-command. With only three days to cover two hundred and fifty miles, the patrol goes on a forced march through hostile Indian territory. After one of the over-anxious soldiers fires on a Sioux lookout as the unit travels through a narrow ravine, John is sent up the ridge to kill the brave in hand-to-hand combat. He does so, only to have his own life saved by Quince, the unit scout, who kills a second Indian. Afterwards, John gives Phil a picture of Celie, stating that it is the only thing he has of her. John does not tell Phil, however, that he had earlier ended his relationship with Celie, knowing that she still loves her husband. Worried about his pregnant wife, Pvt. Arndst Hofstetter convinces young Pvt. Tim Harvey to desert the unit and return to the fort with him, but the two are soon ambushed by a group of Sioux. Hofstetter is saved from certain death by John, though Tim falls prey to a Sioux arrow. With their presence now known, the patrol attempts to quicken their pace. While riding point, Cpl. Arika, a Crow Indian, and Pvt. Doan Moylan, a thief, discover Quince nailed to a stake. Arika is killed attempting to rescue the scout, who dies soon after. While John continues to worry about the men in their dwindling patrol, Phil reminds him that they are only a few men, trying to save the lives of hundreds. With John missing while on point, the enlisted men threaten to mutiny against Phil, only to have the lieutenant return and report that the Sioux have gathered in wait for Custer. Seeing the threat to his authority, Phil challenges John to a fistfight, which ends in a draw. The patrol then heads out, only to discover an ambushed wagon train. The patrol is soon attacked by the Sioux, and Phil is the first to fall. Learning that Custer has yet to arrive at Little Big Horn, the dying commander puts John in charge. He then leads the remnants of the patrol on a direct assault, but badly outnumbered, no one survives.
