Distraught but skilled bounty hunter Gates, accompanied by his horse and faithful dog Zip, tracks three armed escaped convicts into Montana's isolated Oxbow Quadrangle, driven by the fury of his unforgiving ex-father-in-law, Sheriff Deegan, who blames him for his daughter's death. Gates spots the fugitives but before he can close in, he only uncovers a trail of clues: a smear of blood large enough to alarm the sheriff's office, a spent shotgun shell, and an old-fashioned Indian arrow that raises more questions than it answers.
Gates takes the arrow to archaeologist Lillian Sloan, who identifies it as a genuine link to the Cheyenne Dog Soldiers—though Gates suspects there’s more to the story than a simple relic. After delving into library records, he compiles a long list of people who disappeared into the Oxbow, and he uncovers a legend of a “wild child” captured by railroad workers in the early 20th century who escaped and vanished. This fuels his conviction that the three fugitives were killed by Cheyenne survivors who avoided the Northern Cheyenne Reservation and have persevered for 128 years in the northwestern Montana wilderness, striking at anyone who threatens to expose their existence.
Gates convinces Sloan to join him in a search for the missing Cheyenne. The two push into the Oxbow, surviving a string of mishaps and growing closer as they trek deeper into the wild—roughly 50 miles (about 80.5 km) from civilization.
After a week, with supplies dwindling, Sloan proposes turning back. As they prepare to head home, they are suddenly ambushed by a Cheyenne war party. Sloan, speaking Cheyenne, manages to de-escalate the confrontation, and the pair are taken to a Cheyenne village tucked away in a valley reachable through a tunnel behind a waterfall. There they meet Chief Spotted Elk, who recounts the Cheyenne’s escape and survival, and recalls his own run-ins with “the white people” and the years spent in a world of confinement before freedom.
Gates and Sloan gradually begin to earn the trust of the Cheyenne. Yet Yellow Wolf’s young son lies gravely ill, and Sloan persuades Yellow Wolf to permit Gates to ride into town to fetch antibiotics. In town, Gates robs a local pharmacy and is pursued by Sheriff Deegan and other law enforcement. After escaping, Gates reunites with Yellow Wolf in the wilderness, and they return to the Cheyenne encampment. By this time, the sheriff has organized a posse, intent on capturing Gates for the robbery and for Sloan’s whereabouts, threatening the fragile balance between the hunter and the hidden people.
Gates and Sloan continue to grow closer to the Cheyenne, and Sloan reveals that they are indeed the last of their kind. Yellow Wolf shows Gates that the sheriff’s pursuit is closing in. With little choice, Gates proposes a daring escape plan: using some leftover TNT the Cheyenne had once taken from explorers, they will create a distraction and allow the Cheyenne to flee deeper into the Oxbow, living in peace far from civilization. Sloan chooses to stay with the Cheyenne, and Gates reluctantly respects the decision.
The two share a passionate kiss as Gates prepares to set the plan in motion. He surrenders to the sheriff and pleads that he leave the wilderness behind for good. The sheriff discovers the hidden tunnel and moves to enter it. Gates fights for time, attempting to ignite the TNT, but the sheriff blocks him; Yellow Wolf appears, wields his bow, and fires an arrow that detonates the TNT. The blast hurls Gates and the sheriff from the tunnel into the waterfall. Gates saves the wounded sheriff, and the deputy orders everyone to clear out, allowing the pair to be treated back in town.
In Gates’ holding cell, the sheriff presses him for answers. Gates retreats into silence, offering only that some things “deserve to remain undiscovered.” The sheriff’s hard edge softens in reply, hinting at a fragile truce between hunter and lawman. Meanwhile, Sloan and the Cheyenne succeed in escaping, and time passes as Gates begins a solo search for them through heavy snow, guided by hints Sloan left behind. He eventually locates them, and the film ends on a note of reunion: Zip runs toward Gates in a clearing, and he shares a tender, hopeful embrace with Sloan.
