A wendigo kills Kenny Glass and mauls Frank Weaver as the two men make meth in an abandoned coalmine. The mythical monster's bite causes Frank to begin a slow transformation into another wendigo. Believing his feral father can be saved if he completes the metamorphosis, Frank's 12-year-old son Lucas secretly keeps Frank captive inside their remote house, partly to protect his seven-year-old brother Aiden, who eventually begins his own transformation after Frank attacks him.Having left town 20 years earlier to escape an abusive father, recovering alcoholic Julia Meadows returns to Cispus Falls to work as a schoolteacher. Julia temporarily moves in with her brother Paul, the town's current sheriff, which sparks several confrontations due to their troubled childhoods and Julia feeling guilty for abandoning Paul.Based on the boy's disturbing drawings and his strange story about a family of hungry bears becoming monsters, Julia takes an interest in Lucas's wellbeing. While attempting to bond with Lucas and investigating his home life, Julia becomes concerned that Lucas and his brother may also come from a broken family.Native American and former sheriff Warren Stokes finds half of Kenny Glass's mauled corpse while hiking in the woods. Police later locate the other half in the coalmine. Stokes collects an antler and notes native wards hanging throughout the mine.Julia shows Lucas's unsettling illustrations to Principal Ellen Booth. Despite initial reservations about interfering, Ellen agrees to go to the Weaver house and speak to Frank about his son. Upon entering the home, Ellen finds Aiden in an alarmingly disheveled state. Frank savagely slaughters Ellen. A wendigo then bursts out of Frank's body.Classmate Clint Owens tries to bully Lucas on his walk home from school. Now transformed into the wendigo, Frank viciously attacks Clint unexpectedly. Lucas flees home to find his brother Aiden missing and Ellen Booth ripped apart on the floor.Julia tries convincing her brother that Ellen and Clint's disappearances may be connected to Frank Weaver. Paul and his deputy, Daniel LeCroy, briefly visit Frank's house, but leave after finding no one home.Julia goes back to the Weaver house on her own. Finding Ellen's car outside leads to the discovery of her body inside. Paul and the police also find the unusual husk of Frank's human body.Lucas is sent to the hospital to be treated for malnourishment and physical abuse. Julia and Paul argue over Julia's impulse to become Lucas's guardian while his case gets sorted.Julia and Paul take Lucas's drawings to Stokes. Stokes shows the antler he took from the mine as he recounts the ancient legend of cannibalism cursing people to become creatures. Paul finds the wendigo tale too fantastical to believe as an explanation for the brutal deaths.Julia and Paul bring Lucas to their house. Julia tells Lucas that his father died, but Lucas claims his dad was reborn and that as long as he is fed, Frank will love him again. Lucas adds that Frank will come to take him to the mine with Aiden.Noises lead Daniel to investigate the shed outside the Meadows house. Dan finds Aiden hiding just before the wendigo suddenly kills Dan from behind.Paul rushes home in response to Dan's call. The creature violently attacks Paul. As Julia helps her brother recover, Lucas follows Aiden and the wendigo back to the mine.Julia drives to the mine and confronts the creature to save the two boys. Having a change of heart about what really happened to his father, Lucas ultimately helps Julia bring down the monster. Julia cuts out the wendigo's cursed heart.Julia and Lucas observe Aiden undergoing his transformation into the next wendigo. Lucas insists Aiden is merely sick. Julia manages to convince Lucas that it is too late to save his brother. Julia apologetically embraces Aiden before stabbing him to death.Julia and Paul uneasily agree to continue caring for Lucas. However, Paul privately worries the curse may continue when he coughs up discolored blood due to his wendigo wound.