Luther "Yellowstone" Kelly, trapper, surveyor and Indian scout, arrives at the Yellowstone River to board a steamship bound for Fort Buford, where he plans to sell his skins. At the fort, Major Towns, the commanding officer, asks Kelly to scout the Sioux territory south of the Missouri for the Army, and Kelly reluctantly agrees, setting out with Anse Harper, a young man he met on the steamship. As they approach the Snake River, they are captured by Sayapi, a young Sioux, and brought before Gall, chief of the Seven Nations and a hater of whites. Gall reminds Kelly that seven years earlier, Kelly had saved his life after Gall was shot by soldiers and left for dead, and he now demands that Kelly do the same for a captured Arapaho, a beautiful maiden named Wahleeah. Kelly manages to remove the bullet from her spine, and Gall allows Kelly and Anse to leave, despite Sayapi's objections. Later, Wahleeah, having managed to escape from the Sioux, approaches Kelly's cabin half-dead from fever, and when Kelly warns that she will die if she is moved, Gall orders that she remain there until the winter, provoking a jealous outburst by Sayapi. When she revives, Wahleeah asks Kelly to take her to her own people, but he refuses, unwilling to let anything interfere with his trapping. Aware that soldiers are about to cross the river, Kelly warns Major Towns that a thousand Sioux are on the other side, but Towns, eager to punish the Sioux for the massacre at Little Bighorn, orders his soldiers to drive them back to the Dakota Territory. While Kelly is with the soldiers, Anse decides to take Wahleeah back to her people, but in a violent confrontation, Sayapi and his men stop them, and Kelly returns to find his house aflame and Anse dying. An anguished Kelly tracks Sayapi to a cave and kills him, then rescues Wahleeah and tells her he will now return her to her tribe. When Kelly learns that Major Towns died in an attack by the Sioux, and the surviving soldiers are surrounded, he goes unarmed to meet Gall, who offers Kelly his freedom in exchange for Wahleeah, but insists that the soldiers must die. Kelly refuses, and Gall orders the Sioux to attack. When Kelly asks Gall how many more must die, proclaiming that the land no longer smiles on the Sioux people, Gall leaves in frustration. Sometime later, Kelly and Wahleeah ride mules to the river, where he signals a steamship to stop for them.