In an isolated woodland home, a man known only as Daddy – his real name being Gabriel Hanson – keeps Anna locked in an attic, raising her from infancy into her teenage years. He convinces her that the outside world is dangerous, filled with a creature called a 'wildling' that preys on children. As time passes, Anna overhears a conversation between Daddy and Deputy Roger Fowler about their existence, prompting her to test the locked door she knows she cannot open, only to discover it is electrified. Daddy, who uses a match flame to hypnotize her, fills her mind with fabrications, claiming that they are the only two people who exist.
When Anna reaches puberty and dreams of the feral wildling, she becomes terrified of transforming into one herself. To prevent this, Daddy administers daily injections to inhibit her physical development, but the treatments leave her feeling ill and lead her to believe she is dying. In a moment of despair, Daddy contemplates euthanizing her, ultimately turning the gun on himself instead.
Anna awakens in a hospital, where Sheriff Ellen Cooper introduces herself as the one who found her after neighbors reported gunfire. She learns that Daddy survived but is on life support in another room. As she recuperates, Doctor Rooney suggests transferring Anna to a halfway house, a notion met with concern by Ellen, who opposes placing the girl in confinement again. Eventually, Ellen agrees to care for Anna while waiting for DNA results to confirm her identity.
Once at Ellen's home, Anna meets her teenage brother Ray, who teaches her about life’s realities, nurturing a budding attraction between them. But lurking in the shadows is a mysterious figure dubbed The Wolf Man, who shows protective instincts towards Anna.
As Anna delves into her new life, Ellen gradually reveals critical truths, including the unsettling discovery that Daddy is not her biological father. While captivated by the beauty of the Northern Lights during a stargazing session with Ray, Anna's world starts collapsing at a party where an intense moment with Ray leads to a shocking transformation. Following an unexpected incident with school bully Lawrence Fuller, Anna is thrust into a survival struggle that leads to an unexpected fatal confrontation. Caught in a web of violence, she grapples with her identity amidst the chaos.
After fleeing back to her roots, Anna seeks answers, revisiting Daddy's house, but the repercussions of her past actions close in around her. With Daddy scheming and hunting her down, Anna undergoes a harrowing transformation, shedding her sheltered life and embracing her wildling nature. The intense pursuit culminates in a climactic showdown that tests her physical and emotional limits.
In a heart-stopping climax amidst the deep woods, Anna confronts her past and her aggressors. The confrontation leads to a poignant moment of rebirth, as she finds solace beneath the Northern Lights, hinting at new beginnings with the echoes of her wild heritage lingering in the air. As she gives birth, the haunting cry of another wildling can be heard nearby, signifying that Anna's story is just beginning.
