The film tells the tale of two sisters, Violet and Grace, who live a sheltered life within a secluded New England mansion, inherited from their parents. It is heavily implied that their father abused them during their childhood throughout the film, believing that they were "gifted" and home-schooling them whilst practically forcing them to complete recreational activities, such as painting and playing musical instruments, and hurting them either physically or mentally if he was not pleased with their effort. Because of their gloomy childhood, the two sisters have formed a strong bond and are incredibly close, however have also lost touch with reality and often come up with "evil" schemes together, their most recent being to lure a young traveller, whom Violet encounters in a bar, into their home and seduce him. It is never revealed why they have chosen to do this, however it is suggested that the sisters, especially Grace, want a baby to raise together.
Violet catches the eye of the traveller whilst he is with another woman in the bar, and openly flirts with him by dancing gracefully. Enchanted, he abandons his date and leaves with Violet, already drunk. The two return to the mansion, where Violet and Grace flirt with him briefly before dragging him upstairs to the spare bedroom, where he collapses. The next morning, the trio have breakfast together, where the traveller introduces himself as Luke, and the sisters invite him to stay for a few days. He agrees, clearly having taken a liking to Violet. That evening, he invites her for a drive and the two leave Grace on her own for several hours. While out, Luke proposes that they run away together, but Violet laughs this off, claiming he barely knows her and they wouldn't be able to manage with little money. Violet admits that she wants Luke to fall in love with her, but he claims he "doesn't do love". Despite this, the two share their first kiss on the way back. The two return home to find Grace sulking, who claims that Violet is "breaking the rules". Eventually cheering up, the sisters suggest that they play "the alpha game", an activity in which they attempt to connect with Luke mentally after they count him down into the "alpha state". Whilst under, Luke experiences visions of the girls' father and becomes disturbed by this, accidentally strangling Grace after waking up. The next morning, Grace tells Violet that she wants him gone, but she refuses.
Luke continues to push Violet to leave with him, but she cannot bring herself to even consider leaving Grace. Later, the two of them slip away while Grace demonstrates her archery skills and make love for the first time. They begin an intimate relationship, much to the distress of Grace, whose flashbacks become increasingly surreal and intense, a notable one being of her suddenly setting fire to a box of matches without touching them after her father had been trying to get her to move a flame in the same manner, and she begins to lose her mind. Luke begins experiencing visions of the girls' father as well, and decides to leave the mansion alone after Violet refuses to come with him. Grace attempts to reconnect with her sister, but Violet becomes depressed after realising she loved him. Meanwhile, Luke encounters his girlfriend from the beginning of the film and they briefly reconcile, however he realises afterwards that he is in love with Violet, and decides to return to the mansion. Despite Violet's happiness, Grace grows incredibly jealous and begins cutting herself at night.
After discovering that she is pregnant, Violet finally agrees to go away with Luke, ignoring Graces' warnings. In a final attempt to get her sister back, she hatches a plan to seduce Luke while Violet is out. Showing minimal restraint, Luke sleeps with her, but regrets it immediately afterwards and begins to hate Grace, who doesn't hesitate in revealing what happened between them. Distraught, Violet runs out of the house but Luke follows her and apologises. The two decide to leave there and then, driving away as Grace watches from the window. The couple stay in a motel overnight, where Violet reveals her pregnancy. Luke concludes that he is happy and promises to get a job. The next morning, they begin making their way to California, however Violet drives back to mansion whilst he is asleep. Luke is furious that they are back, but after Grace calls a truce, he agrees to stay for one more night. Violet goes to the market to buy some supplies for a "celebratory feast", while Grace tells Luke about a painting of him that she needs him to pose for so she can finish it.
Grace has Luke stand on a table with his hands tied behind his back, and begins painting. Whilst doing so, she begins to hear her father's voice again, and it is here that the extent of her insanity is revealed. It is confirmed by a film that Grace is projecting onto the wall that their father abused them, showing him pushing her into their swimming pool and filming her struggle. Grace begins crying as she suffers severe flashbacks, gripping the paintbrush so tightly that her hand starts bleeding, as well as picking up her bow and arrow and pointing it at Luke. Having had enough, Luke snaps at her, telling her she is crazy, and attempts to escape, knocking over a candle as he does so, which sets the paintings alight. Grace has the same flashback about trying to move the flame with her mind, and fire grows as she hears her father's words, possibly proving her telekinesis, and suggesting that this is her final attempt to get rid of Luke. Violet senses something is wrong and returns to the mansion - just in time to see Luke die in the fire. Grace escapes unharmed.
After Violet has a miscarriage in the bath, she finally decides to leave the mansion once and for all. It is revealed that Grace is now pregnant, suggesting that she got what she wanted all along. The film ends with a heavily pregnant Grace knitting a babygrow. Her father appears next to the cot she has out prepared, but as she walks over she simply opens a window and goes back to her knitting, suggesting she has finally moved on from her childhood.Alicia Silverstone as Violet
Sienna Guillory as Grace
Joe Anderson as Luke
Leigh Lawson as Father
Vaida Butyte as Mother
Jessica Suffield as Young Grace
Elizabeth Pliuchkina as Young Violet
Melanie Giliati as Gee Gee
Dan Crawford as Concierge