The narrative opens with Grace crawling on all fours through tall dry weeds like a predator, clutching a large butcher knife, watching her infant lying in a basket on the grass, immediately establishing her deep psychic fracture. Flashbacks and early scenes reveal Grace and Jackson’s past: an intense, animalistic, sexually charged couple who relocate from New York to an isolated Montana homestead formerly owned by Jackson's uncle, who died by suicide in the home. Grace aims to write a novel, while Jackson intends to make music and tend the land.
Following childbirth, the domestic structure collapses. Grace cannot write a line, the sex that anchored their relationship vanishes, and Jackson pulls away emotionally. Grace is left alone in the derelict house, haunted by loneliness and auditory hallucinations, while visits from Jackson's sleepwalking mother Pam and dementia-plagued father Harry underline an atmosphere of decay. Grace begins hallucinating and obsessing over Karl, an enigmatic local motorcyclist, leading to reckless, hypersexual behavior and an agonizing fight with Jackson born of unmet lust and violent resentment.
In the climax, an encroaching summer wildfire spreads through the timberland. Grace strips off her clothes and walks straight toward the blazing forest wall. Blending sensory hallucination with reality, Grace does not perish in the flames, but is found burned, feral, and catatonic, leading to her institutionalization. As she stares into the void of the psychiatric facility, the film cuts to black, accompanied by Lynne Ramsay singing "Love Will Tear Us Apart," cementing that Grace’s love was so absolute that its collapse burned away her reality.