On her 18th birthday, India Stoker (Mia Wasikowska)—a girl with a strong acuteness of the senses—has her life turned upside down after her loving father Richard (Dermot Mulroney) dies in a horrific car accident. She is left with her unstable mother Evelyn (Nicole Kidman). At Richard’s funeral, Evelyn and India are introduced to Richard’s charismatic brother Charlie (Matthew Goode), who has spent his life traveling the world. India, who didn’t know Charlie existed, is perturbed by his presence. He announces that he is staying indefinitely to help support India and Evelyn, much to Evelyn’s delight and India’s chagrin.

Shortly after, India witnesses Charlie argue with Mrs. McGarrick (Phyllis Somerville), the head caretaker of the house. Mrs. McGarrick complains to Charlie that she has been his “eyes and ears” since he was a boy. Mrs. McGarrick then disappears. Charlie and Evelyn grow intimate while India continues to rebuff his attempts to befriend her. Later, her great aunt Gwendolyn (Jacki Weaver) visits the family, much to Evelyn and Charlie’s dismay. At dinner, Gwendolyn shows surprise at Charlie’s claims of traveling the world and tells Evelyn that she needs to talk to her about Charlie.

Gwendolyn ends up changing hotels due to an unexplained fear and suspicion of Charlie. However, she loses her cell phone and tries to call the Stokers’ home from her hotel payphone. Charlie corners her in the phone booth and strangles her to death with his belt. Meanwhile, India discovers Mrs. McGarrick’s body in the freezer and realizes Charlie is a murderer.

India unleashes her inner aggression at school and stabs a bully, Chris Pitts (Lucas Till), in the hand with a pencil after he tries to land a surprise punch to her head. This draws the attention of another classmate, Whip Taylor (Alden Ehrenreich). India goes home and witnesses Evelyn and Charlie growing intimate. She wanders off to a local diner where she runs into Whip. She and Whip go into the woods where they proceed to make out until India aggressively bites him. Whip attempts to rape India until Charlie intervenes, and breaks Whip’s neck with his belt while Whip’s body lies on top of India. India aids Charlie in burying the body in her garden. She attempts to call Gwendolyn, but hears her phone ring in the garden, realizing Charlie killed her too. India takes a shower and masturbates to the memory of the murder, climaxing as she remembers Charlie breaking Whip’s neck.

While going through Richard’s office to gather things of his she wants to keep, India discovers that a key she received as a birthday present belongs to a locked drawer to Richard’s desk. Inside, she finds dozens of letters Charlie wrote to her over the years, which detail his travels and his love for his niece, although they have never met. However, she sees that the sending address is a mental institution. She confronts Charlie, who explains the truth: Charlie murdered his and Richard’s younger brother Jonathan as a child by burying him alive in a sandbox because he was jealous that Richard paid more attention to him. He was then put in a mental institution. When released on India’s 18th birthday, Richard gives Charlie a car, money, and an apartment in New York City on the condition that he stay away from Richard’s family. Feeling hurt and betrayed, Charlie beat Richard to death with a rock and staged the car accident.

At first, India is in shock and angered but Charlie explains he has come for her then gives her a birthday present, a pair of stiletto heels. She seemingly forgives Charlie and grows closer after he provides an alibi for her when Sheriff Howard (Ralph Brown) questions her about Whip’s disappearance. They grow close to intimate before Evelyn witnesses them. Charlie proceeds to tell India that he wants her to come to New York with him and that he had waited for her until her 18th birthday so she is now of age. Later, Evelyn coldly expresses her desire to watch India suffer before confronting Charlie, implying that she knows the truth about Richard’s death and Charlie’s stint in the mental institute. Charlie seduces Evelyn and then attempts to strangle her with a belt before India fatally shoots him with a rifle. She then buries Charlie’s body in the backyard and then she leaves for New York in his car.

India is pulled over for speeding by Sheriff Howard, who asks her why she’s in a hurry. She replies that she wanted to catch his attention, then plunges a pair of pruning shears into his neck. She pursues the wounded sheriff into a field to dispatch him with her rifle.