John Ottway (Liam Neeson) works in Alaska killing the wolves that threaten an oil drilling team. We see a scene of him shooting a wolf and then watching, with his hand on it almost as though he's sorry for it, as it breaths more and more slowly and finally dies. On his last day on the job, Ottway writes a letter to his wife Ana (Anne Openshaw) who has left him, that he plans to commit suicide. While holding the barrel of the Winchester Model 70 in his mouth, Ottway hears the howl of a wolf, which stops him.
Upon completing the job, the team and Ottway head home on a plane that crashes in a blizzard. Ottway then sees a vision of his wife but awakens to find one of the team, Lewenden (James Badge Dale), mortally wounded. Ottway calms him, letting him know that he is going to die, and then Lewenden dies peacefully.
Ottway sets the survivors to task collecting material for a fire. He sees a woman in need of help, but finds her being eaten by a gray wolf who also attacks Ottway. He is rescued by the others and explains that they are most likely in the wolves' territory. After starting a fire, the survivors take turns keeping watch. While urinating, Hernandez (Ben Bray) is killed by two wolves. The remaining survivors find his body in the morning and Ottway suggests they leave the crash site because they are wide open to attack. Diaz (Frank Grillo) questions Ottway's leadership and begins defying his orders. Before they leave, Ottway and the others remove the wallets from many of the bodies with the intention of returning them to surviving family members. Hendrick says a prayer and thanks to God for allowing them to survive the crash and then the survivors leave the crash site.
While hiking across the snow, Flannery (Joe Anderson) falls behind and is killed by three wolves. The remaining survivors continue on and make camp in the woods, where tension between Ottway and Diaz comes to a head as the survivors create makeshift weaponry. Diaz threatens Ottway with his knife, but is disarmed by Ottway. The survivors meet the alpha wolf, who sends an omega to test Diaz. However, the survivors are able to kill the wolf and eat it. Diaz severs its head and throws it back as a symbol of defiance.
The group stop to build a campfire at night and they start a conversation. Diaz tells the group how the men who died aren't in heaven and there is no god, Talget admits that he believes but Ottway confesses that he too is an atheist, but he wishes that he could believe. Burke (Nonso Anozie) awakens and he begins to hallucinate from hypoxia. He goes back to sleep in front of the campfire. The group bonds over personal stories. A blizzard approaches and they try to preserve the campfire to prevent hypothermia. Despite their best efforts, Ottway finds Burke's frozen lifeless body in the morning.
Further in their travels, the survivors come across a high canyon wall within which, screened by trees, they identify a river. Hendrick (Dallas Roberts) jumps to the trees to secure a line as a means of traverse. Diaz and Ottway make it across the line to join Hendrick, but Talget (Dermot Mulroney), who is afraid of heights, loses his glasses on the way and freezes out of fear. He reluctantly continues across, but soon finds his injured hand has begun bleeding and he gets caught up in the makeshift rope. Talget struggles to untangle himself, but the line breaks and he crashes through the trees to the ground. Wounded, Talget sees a vision of his daughter and is dragged away by the wolves. While attempting to save Talget, Diaz falls from the tree and injures his knee.
The three remaining survivors continue their trek and make it to the river, but an exhausted Diaz can make it no further, preferring to stay and die than go on. Hendrick tries to convince Diaz to carry on, but Ottway tells him it is futile. They give each other final goodbyes and Ottway and Hendrick leave Diaz on the riverside, as the crackling of branches caused by wolves is heard.
Ottway and Hendrick continue, but are soon chased by wolves again. Fleeing, Hendrick falls in the river and he gets his foot stuck between underwater rocks. Ottway jumps into the river to attempt to save him but Hendrick drowns in the river. Freezing and alone, Ottway then curses God and asks for His help with no response.
Ottway continues on without his wet coat but he is eventually dazed from hypothermia taking effect. He then stops and pulls out each wallet collected from the dead, examines the mementos they contain, and places them in a pile on the snow, adding his own wallet as well. Suddenly, the pack of wolves surrounds him, leading Ottway to discover that he has walked right into their den. He is soon spotted by the alpha wolf and realises that it is female while the other pack members back off. Ottway sees another vision of his wife, which now reveals that she was dying on a hospital bed, and suggests the reason for his earlier attempted suicide. Deciding to make a stand, he tapes broken miniature alcohol bottles to his fist and a knife to his other hand. He recites his father's poem aloud to himself, then charges the alpha wolf before the screen goes black. In a post-credits scene, the back of Ottway's head is seen laying on the side of the presumably dying Alpha wolf's stomach, as it breaths more and more slowly, a bookend to the similar scene at the beginning.