Plot
Sylvie Cooper is a young girl at a private school for the wealthy. At a local hangout, she first meets Ivy, a street-smart but poor girl, and witnesses Ivy mercy-killing a heavily wounded dog.
In their second meeting, when Sylvie's father Darryl comes to pick her up, Ivy asks for a ride, and Darryl reluctantly agrees. Ivy makes an excuse to sit in the front with Darryl. She puts her feet on the dashboard and deliberately allows her mini-skirt to fall back onto her hip, revealing her legs, which Darryl notices.
A few weeks later, Sylvie invites Ivy to her house. She tells Ivy that Darryl is her adoptive father and that her biological father is African-American. She also says that she once tried to kill herself. They meet Sylvie's sickly mother, Georgie, whom Ivy later wins over by talking about her scholarship and helping her unblock her oxygen tank.
Soon after, as both of Sylvie's parents enjoy Ivy's company, they practically allow Ivy to move in. Ivy and Sylvie share clothes and sleep in the same bed. As they have similar figures, Georgie lends Ivy some of her clothes.
In an attempt to improve his failing career, Darryl decides to throw a party at his house, and enlists Sylvie to help him. However, Sylvie is needed at work on the night of the party, which is orchestrated by Ivy so that she will be the one to assist Darryl. After the party, she dances with Darryl in the kitchen and they hug. Georgie walks in on them and storms upstairs. Ivy apologizes to Georgie and claims that Darryl was under stress and she was only comforting him. Georgie believes Ivy, accepts a glass of champagne drugged with sleeping pills, and falls asleep. Ivy sits on the bed next to Georgie and begins to massage Darryl's crotch with her foot. It is implied that he performs oral sex on Ivy and she climaxes.
Over the next few days, Ivy continues changing her appearance and wears Georgie's clothing more often. Sylvie becomes increasingly irritated with Ivy for her growing presence in her family, and her anger reaches a breaking point when even her dog chooses Ivy over her, which in fact is because Ivy has some dog treats in her pockets. Sylvie skips school and tries to spend some time alone. Darryl picks Ivy up and drives them into the forest, where they drink and have sex.
The next morning, Georgie plays a cassette tape that Sylvie made for her and walks out onto her balcony. Ivy walks up behind Georgie, talks to her and without warning, pushes her off the balcony to her death. Because Georgie is known to have a mental illness, and has threatened to commit suicide previously, Ivy is not suspected. A few weeks later, Sylvie talks Ivy into going for a ride in her mother's sports car. When Sylvie becomes suspicious of her involvement in Georgie's death, Ivy crashes the car, then moves the unconscious Sylvie into the driver's seat.
In the hospital, Sylvie hallucinates that her mother is sitting in front of her. This inspires her to get back to her house in an attempt to save her father from Ivy. When she gets to her house, there is a raging storm. She runs inside to get out of the rain, experiencing hallucinations all along the way. When she gets inside, she sees Darryl and Ivy having sex, and flees the room.
As Darryl runs outside to look for Sylvie, Ivy runs out after him, accidentally revealing that she was behind the wheel; due to scarring on her chest. She lies, claiming that it was to protect him. He drives off to find Sylvie and Ivy goes up to Georgie's old room, plays the tape Sylvie made for Georgie, wears Georgie's robe and walks out to the balcony. Sylvie sees Ivy and, because of her head injury, believes that it is her mother and makes her way to the balcony. Sylvie tells Georgie that she loves her and Georgie says she loves Sylvie too. When they kiss, Ivy begins to use her tongue, which breaks Sylvie out of her hallucination. Ivy says Georgie wanted to die and now the three of them can be a family. Sylvie rejects her delusion and pushes Ivy over the balcony, but Ivy holds onto Sylvie's necklace in an attempt to take Sylvie with her. Her attempt backfires, as the chain breaks, and a screaming Ivy falls to her death alone. Darryl returns to see Ivy's corpse on the ground with Sylvie above.
The film ends with Sylvie narrating that she still loves and misses "her", following the parallel between Ivy and Georgie.
