A blossoming teenager uncovers the dark secret behind her traumatic childhood.
Anna spends her entire childhood under the care of a mysterious man she only knows as Daddy. He keeps her locked in an attic making her fear the Wildling, a child-eating monster that roams the outside. At age 16, Anna is freed by small-town sheriff Ellen Cooper who helps her start a new life as a normal teenager. But as Anna's body begins to blossom, her childhood nightmares return with a vengeance, leading to the conclusion of a terrifying secret.
Anna is a young woman who spent her entire childhood locked in the attic of her house, under the care of a mysterious man she called father. One day Ellen Cooper, the town sheriff frees Anna and helps her start a new life by receiving her at home, but childhood nightmares about creatures that devour children interrupts the possibility of Anna's normal life.
- 'Daddy,' whose real name is Gabriel Hanson, keeps Anna locked in the attic of his isolated woodland home. Raising her from infancy into a teenager, Daddy convinces Anna that she can never go outside for fear of a 'wildling' that eats children.
Anna overhears Daddy speaking to Deputy Roger Fowler. Anna tries turning the knob on her door to find it electrified. When Anna asks about the other man, Daddy tells her that they are the only two people who exist. Daddy uses a match flame to hypnotize Anna as he continues filling her mind with fiction.
Anna begins puberty after having a dream about a werewolf-like wildling mauling an animal in the forest. Intent on preventing a transformation that would reveal Anna is actually a wildling, Daddy begins giving Anna daily injections to prevent her body from maturing.
As the injections make her sick, Anna becomes convinced she is dying. Daddy considers euthanizing Anna with a handgun, but shoots himself in the mouth instead.
Anna wakes in a hospital where she sees the outside world for the first time. Sheriff Ellen Cooper introduces herself to Anna as the woman who rescued her after neighbors reported hearing a gunshot at Daddy's home. Anna asks about Daddy. Ellen shows Anna that Daddy survived and is on life support in another room.
After she recovers, Doctor Rooney recommends discharging Anna to a halfway house, which Roger supports. Ellen objects to essentially locking up Anna again. When Anna expresses wanting to go home with Ellen, Ellen agrees to take the girl pending the results of a DNA test to discover her identity.
Anna meets Ellen's teenage brother Ray, who lives with Ellen. Over time, Anna learns the truth about procreation, death, and other fundamental aspects of real life from Ray. Anna also begins attending school, studying, menstruating, eating meat, and developing a mutual attraction with Ray.
A grizzled man wearing a wolf skin and known only as 'The Wolf Man' stalks Anna as she chases a deer in the forest. The Wolf Man prevents Anna from triggering a hunter's trap. Afterward, Anna begins researching animalistic predators.
While shaving Anna's legs as she continues teaching her about womanhood, Ellen reveals that the DNA test showed Daddy is not Anna's real father. Anna becomes fascinated with the Northern Lights, and asks Ray about them when they stargaze together.
Anna and Ray attend a party thrown by their classmate Jen. Anna's mouth begins bleeding after kissing Ray during a romantic moment. Anna retreats to the bathroom where several teeth fall out. Frightened, Anna sneaks out of the house and escapes into the woods.
School bully Lawrence Fuller attempts to sexually assault Anna in the woods. While experiencing a vision that she is being attacked by a vicious wildling, Anna savagely kills Lawrence.
Anna returns to Daddy's house and spends the night in her old room with the barred window. Ellen finds Anna walking in town the next morning, although Anna refuses to say what happened.
Roger comes to Ellen's house to report that Lawrence Fuller was found murdered. Ellen questions Anna about Lawrence's death, but Anna remains silent. Ray asks to speak with Anna alone to find out what happened after the party. When Ray sees Anna's missing teeth, he goes to get Ellen to take Anna to the hospital. Anna uses the opportunity to flee the house.
Anna meets the Wolf Man in the forest again. From a flashback as well as the Wolf Man's story, it is revealed that local hunters purged the town of wildlings 16 years ago. However, Daddy couldn't bring himself to kill Anna when he discovered her as an infant in a wildling cave. Thinking he could prevent her transformation, Daddy instead decided to raise Anna in secret.
Anna sneaks into the hospital to see Daddy. Anna runs away when Daddy turns to look at her.
Anna returns to Ellen. Ellen reluctantly cuffs Anna and puts her in jail for Lawrence's murder.
With Roger serving as Anna's guard, Daddy comes to see Anna. Daddy passes Anna a syringe and convinces her to inject herself with an unknown substance. When Anna asks why Daddy spared her and never told her she was a wildling, Daddy tells her it was a mistake. Daddy leaves.
Anna escapes when Ellen unlocks her cell the next morning. Anna forces Ray to drive Ellen's patrol vehicle as a getaway car. When Anna exclaims that she wants to go all the way to the Northern Lights, Ray stops the car. Anna flees into the woods. Ray follows her. Anna and Ray end up having sex.
Daddy and Roger organize hunters to go after Anna. When Ray gets shot, Anna has him go back without her while she retreats deeper into the forest. Ray regroups with Ellen while Anna gradually begins growing feral.
Anna goes missing for several months. Ellen and Daddy separately continue their searches for the girl.
Ray sees Roger filling a large number of gas cans. Ray calls Ellen to warn that the hunters appear to have a lead on Anna.
Anna kills several hunters attempting to shoot her in the woods. Ellen arrives near Anna's location. Roger tries taking Ellen at gunpoint, but Anna kills him. Anna indicates that she is pregnant with Ray's child before fleeing back into the forest.
Daddy sets a forest fire that traps Anna in a mountain cave. Daddy confronts Anna. Daddy begins cutting open Anna's stomach to remove her child when she suddenly fights back. Anna transforms further into a wildling and bites Daddy's neck. Daddy dies. Anna collapses.
The Wolf Man stitches up Anna's stomach and helps her recover. Ellen and Ray spot Anna in the woods across a lake, but let her go. Anna makes it to the Northern Lights where she gives birth. Anna hears another wildling cry in the distance.