Our story begins with the Rocky Mountain Fur Company. While trapping beavers along the Missouri River, the group gets involved in a battle with the Arikara tribe, a battle that eventually ropes in the U.S. Army. To everyone's surprise, the much larger U.S. force gets crushed by the Arikara, who then take control of the region.
Despite this, the company sends out a group led by Captain Andrew Henry to continue trapping. The expedition is tense from moment one, but it gets way worse after Hugh Glass, one of the toughest dudes on the team, is attacked by a bear. Although he manages to kill it, Glass looks like he's gonna die from his wounds.
After a failed attempt to drag Glass along with them on a stretcher, Henry offers to pay two men to stay behind with Glass while he dies, after which they'll meet back up with the group. John Fitzgerald, a skeevy, violent fellow, and Jim Bridger, a nervous nineteen-year-old, volunteer.
It quickly becomes clear that Fitzgerald is up to no good—he just wants Glass's prized rifle, the Anstadt. For his part, Bridger tries to help Glass but is intimidated into inaction by the older man. After a few days of this, Fitzgerald notices a group of Arikara warriors nearby and decides to scramble, taking Glass's gun and supplies before leaving. Bridger follows.
But Glass isn't dead. He slowly regains the strength to move and begins crawling toward Fort Brazeau, where he hopes to resupply before going after Fitzgerald and Bridger. He survives by eating small animals and plants but hits the mother lode when he finds a pack of wolves eating a buffalo carcass. He scares them away using a torch made of sage branches and enjoys a few days of rest, relaxation, and lots of eating.
After this recharge, Glass comes across a destroyed Arikara village, where he finds an old, blind woman. He makes her a meal, and she dies the next morning. As he builds her a funeral pyre, he's approached by a group of Sioux warriors—traditional enemies of the Arikara. Their leader, Yellow Horse, brings Glass to a medicine man, who heals Glass's infected wounds. Afterwards, Yellow Horse escorts Glass to Fort Brazeau.
At Fort Brazeau, Glass befriends Kiowa Brazeau, a keenly intelligent French trader. Kiowa introduces him to a group of voyageurs and suggests that Glass accompany them north on their boat. Glass agrees. Unfortunately, the rest of the group is killed by an Arikara assault, and Glass is forced to travel the rest of the way to Fort Union (where Captain Henry was headed) alone.
Fort Union is empty, but Glass quickly realizes that the group had gone to a Fort Manuel in Yellowstone instead. He arrives there on New Year's Eve. When he sees Bridger, he immediately attacks him, but he stops when he realizes that the young man isn't resisting. After calming down, he learns that Fitzgerald had stolen pelts from Henry and headed for Fort Atkinson.
After another ill-fated boat trip that ends in another Arikara attack, Glass finally arrives at Atkinson. He learns that Fitzgerald has joined the army, which means that he'll have to take his claim to military court rather than just settle it with a pistol. Of course, Glass decides to just settle it with a pistol, anyway, shooting Fitzgerald in the shoulder when it becomes clear that he'll be found innocent.
After this incident, Glass is thrown into jail. He's bailed out by Kiowa, who begs him to embrace life rather than waste it by going after Fitzgerald again. To our surprise, Glass seems to accept this suggestion.
Meanwhile, Jim Bridger, inspired by Glass's example, asks Henry to be sent on an expedition deep into the wilderness. Henry agrees.