During an intense storm, a woman named Emma Parker suddenly stumbles into a local store, disoriented and affected by the raging elements outside. The butcher, surprised by her state, tries to engage her, noting that things are likely to become more chaotic before there’s any relief. After making a few purchases, Emma notices a poster advertising missing teenage girls hanging ominously on the wall. Tragically, as she approaches her vehicle, she begins to bleed from her mouth and falls into a slippery ditch, hitting her head, leading to an unfortunate drowning.
In the aftermath of this devastating event, Sheriff Meeks somberly informs Frank Parker, Emma's husband, about her tragic death. Overwhelmed by sorrow, Frank is unable to muster the strength to identify his wife’s body, opting instead to send their two daughters, Rose and Iris, in his place. During a mandated autopsy, Doctor Barrow—who previously assisted with the birth of Frank's son Rory—discovers alarming signs of Kuru disease within Emma's remains. Meanwhile, Frank finds solace in his compassionate neighbor, Marge, but his emotional state takes a sinister turn when, while driving through the relentless storm, he encounters a stranded motorist whom he implicitly attacks with a tire iron.
As the narrative unfolds, interspersed scenes depict Rose and Iris questioning their preparedness to assume their mother’s religious responsibilities. Despite their doubts, Iris insists on honoring the yearly ritual. Their saga is occasionally mirrored with tales from the past, chronicling the hardships faced by their pioneering ancestors as winter pressures them to make dire decisions for survival. The siblings struggle with the weight of their heritage, grappling with terrifying familial traditions and a father whose mental state seems to be spiraling out of control.
In a shocking twist, Rory discovers a young woman imprisoned within his father's shed — an act of cruelty that Frank demands remain a family secret. Under duress, Rose and Iris are coerced into committing an unfathomable act: killing and consuming the young captive. A visit from Marge, who attempts to provide a vegetarian meal, reveals a chilling atmosphere in the Parker household when she feels an eerie presence and unwittingly causes tension with Iris.
In the threadbare past reimagined, the family's struggles mount as they take refuge in a cave—fearful for their father's sanity as he isolates himself and cries. An unsettling moment occurs when he ties up a deceased woman, possibly their mother, compelling one of his daughters to wield a knife upon her body, symbolizing humanity’s darkest instincts in survival situations.
Suspicion grows when Doctor Barrow, haunted by the disappearance of his daughter, finds a disturbing bone fragment in the creek. Though Sheriff Meeks dismisses his fears, the Deputy, Anders, succumbs to the tension of unreciprocated feelings for Iris and allows emotional chaos to unfold. An intimate moment culminates in tragedy when Frank discovers their coupling, leading to a catastrophic confrontation that leaves Anders dead and Iris heartbroken.
As the plot thickens, Frank restricts his daughters to their room while muttering their family traditions. As he cooks dinner using mysterious powders, Rose becomes aware of his sinister intentions to poison them. In a desperate act to save her siblings, she attempts to thwart their father’s deadly scheme by alerting Iris and preventing Rory from eating.
The confrontation reaches a climax when Doctor Barrow, equipped with newfound knowledge of the Parkers’ horrifying secrets, confronts Frank, only for the encounter to escalate into brutal violence. In a chaotic sequence of events, Frank finds himself overpowered, and a violent rebellion emerges from Rose and Iris, uniting to combat their father’s tyrannical grip on their lives.
As the dust settles, the siblings’ vicious act leads to Frank’s demise while leaving Doctor Barrow, horrified yet alive to bear witness to the unsettling reality of family betrayals and the cycle of violence. In the heart-wrenching aftermath, Rose, clutching a diary filled with their ancestors' cannibalistic memories, embarks on a poignant journey with her siblings, determined to leave their haunted past behind and seeking a semblance of freedom from the horrors that have plagued their lives.
