Plot
In 1995, a hiker's vanishing in the remote mountains of Oregon sparks speculation about a virus transmitted by the region's wildlife, dubbed "hill fever" by locals but called ma'iingan odengwaan, or "Face of the Wolf", by earlier Native American tribes. During a hunting trip in the area, a young Blake Lovell spots a mysterious humanoid creature. His father Grady takes him to hide in an elevated hunting blind. Later that night, Grady radios his friend Dan Kiel about the beast, implied to be the infected hiker.
Thirty years later, Blake lives in San Francisco with his daughter Ginger and wife Charlotte, a journalist. Like his now-estranged father, he struggles to control his temper, and his marriage is strained. One day, he receives a death certificate for Grady, who went missing, and the keys to his childhood home. He decides to vacation there to pack up his father's belongings and try repairing his marriage.
Seeking directions in the forest, the family encounters Dan's son, Derek, who leads them to the house. Before they arrive, Blake swerves at the sight of a creature like the one he saw as a child. The creature scratches Blake's arm and kills Derek. Blake frantically leads his family to the house, barricading the entrance as the monster searches for weak spots. With his arm infected, Blake starts losing teeth and experiencing noise and odor sensitivity. The monster attacks Blake again through a pet door before Charlotte repels it with a hammer.
After Blake passes out and wakes up, Charlotte discovers he has lost some motor functions and his ability to speak and understand human language. He develops canine teeth and night vision, his hair thins on his head and grows in patches on his body, and his skin blotches. Before the family can drive away in Grady's old truck, the creature smashes the windshield, revealing itself as a werewolf and forcing them to seek shelter atop a greenhouse. Blake signals Charlotte to take Ginger back to the house and makes the monster follow him into the forest.
A limping and more deformed Blake soon returns. He tries to play a game with Ginger before he vomits one of the werewolf's fingers and menaces Charlotte. Regaining control, he prepares to leave to keep his family safe from the danger he is becoming, but the werewolf tackles him. In the ensuing battle, the monster acknowledges Blake as he fatally bites its throat. Recognizing a military tattoo on its arm, he realizes the werewolf is Grady. Outside, Blake undergoes his final skeletal changes, with claws forcing out his fingernails, and his vision becomes warped. Still self-aware but unable to restrain his primal instincts, he breaks back into the house. Charlotte slashes his hand with a knife and escapes with Ginger.
Blake claws his way into a barn and is caught by a foothold trap Charlotte laid down. He chews off his ensnared foot and continues pursuing his family, who hide in Grady's hunting blind as the sun rises. Charlotte holds her approaching husband at gunpoint, and Blake motions for her to shoot. Ginger, described earlier as always able to tell what her father is thinking, affirms that Blake is in pain and wants to die. Blake breaks through the door, and Charlotte fatally shoots him. The dying Blake enjoys the comfort of his family, who look out into a beautiful valley he once described seeing as a child.
