Sylvie Cooper (Sara Gilbert) is a teenage girl at a private school for the wealthy. She first meets Ivy (Drew Barrymore), a street smart but poor and trashy girl, at a local hangout where Ivy enjoys rope-swinging from a tree. A young boy runs up and says, "Come on! A dog got hit!" Sylvie kneels next to the still-breathing dog, when all of a sudden Ivy crushes the dog's skull with a pipe to put it out of its misery.
While sitting in the office for phoning in a bomb threat to a local television station that her father works for, Sylvie sees Ivy walk in and begins to talk to her. Later that day, when Sylvie's father picks her up, Ivy asks for a ride. At first, Sylvie's father Darrel (Tom Skerritt) is reluctant, but he grudgingly compromises. Ivy tells Sylvie she gets car-sick and asks to ride in the front. This is actually a ruse to get nearer to Darrel, as Ivy has an interest in older men. Ivy puts her feet on the dashboard and allows her mini-skirt to fall back onto her hip, revealing her legs. Darrel notices this.
A few weeks later, after Sylvie is no longer grounded, she and Ivy meet again at the same hangout. They walk to Sylvie's house together. On the way, Sylvie tells Ivy that Darrel is her adoptive father and that her biological father is African-American. She also says that she once tried to kill herself. Sylvie invites Ivy into her parents' mansion. They walk into the living room which overlooks the San Fernando Valley. Ivy says that if she were to kill herself, she'd like to fall. Sylvie's sickly mother, Georgie (Cheryl Ladd), walks in on their conversation, and it turns out that Sylvie was actually lying about her attempted suicide and her father. Georgie does not want Sylvie to be friends with Ivy initially, but Ivy later wins Georgie over by talking about her scholarship and helping her unblock her oxygen tank.
In the narration, Sylvie explains that Georgie liked Ivy's energy and both of her parents enjoyed Ivy so much that Ivy practically moved in. Ivy and Sylvie share clothes and sleep in the same bed, and when Georgie offers to lend Ivy some of her clothes because of their similar figures, Ivy begins to wear the expensive clothes.
After a spat with her parents, Sylvie says she wants to do something to "make her parents cringe," and Ivy convinces her to get a tattoo so that "they can be like blood sisters."
Darrel decides to throw a party at his house to try to improve his failing career, and he enlists Sylvie to help him. When Sylvie's boss at the charity center calls, Ivy picks up the phone and tells him that Sylvie can work the night of the party, which allows Ivy to fill in with helping Darrel. She straightens her hair and wears one of Georgie's dresses. That night, after the party, she dances in the kitchen and then begins to dance with Darrel. Georgie walks in on them and storms upstairs. While Georgie and Darrel are sitting together, Ivy walks in and apologizes to Georgie, claiming that Darrel came into the kitchen to cry, and that she was only hugging him to make him feel better. Georgie believes her and accepts a glass of champagne from Ivy. She then falls unconscious because of the pills Ivy put into the champagne beforehand. Ivy sits on the bed next to Georgie and begins to massage Darrel with her foot while he kisses her legs.
Ivy appears to change over the next few days. She continues to straighten her hair and wears more and more of Georgie's clothing. Sylvie becomes increasingly irritated with Ivy and throws a fit when she finds Ivy with her dog in Georgie's sports car. She makes Fred (the dog) choose between her and Ivy. Ivy cheats and shakes the treats in her pockets while she calls Fred. That day, Sylvie skips school and tries to spend some time alone to sort things out in her head. Darrel picks Ivy up and they go out into the forest where Ivy gets Darrel drunk and they have sex.
The next morning, Georgie plays a record that Sylvie made for her and walks out onto her balcony. Ivy walks up behind her and begins talking to her.
Then, without warning, Ivy pushes Georgie off the balcony and makes it look like a suicide, which Georgie had regularly threatened about.
A few weeks later, Sylvie washes Georgie's old sports car and Ivy walks up with the urn holding Georgie's remains. She suggests that they take a ride as a final goodbye to Georgie. While she's driving, Ivy begins to hum the song that Georgie was playing the morning Ivy pushed her. Sylvie confronts her and Ivy crashes the car to avoid answering. She moves Sylvie into the driver's seat to incriminate Sylvie.
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 Darrel and Ivy having sex and flees the room.
Darrel goes to look for Sylvie and tells Ivy to stay inside. Ivy goes up to Georgie's old room and puts in the tape that was playing the morning Georgie died. She puts on Georgie's robe and walks out onto the balcony. Sylvie is sitting outside in the storm and sees the light, and because of her very serious head injury, believes that it is her mother on the balcony. She goes up to the room. Sylvie sees her mother turn around from the balcony.
Sylvie tells Georgie that she loves her and Georgie says she loves Sylvie too. They kiss, but when Ivy begins to use her tongue, Sylvie comes out of her hallucination and sees that it is really Ivy. Ivy says how her mother wanted to die and lovingly says how they can all be a family now. Sylvie pushes Ivy off her and onto the balcony, at which point Ivy says how she will take Sylvie with her over the balcony. Ivy almost falls off the balcony, but manages to keep from falling by holding onto Sylvie's necklace. The chain breaks and Ivy falls to her death while still clutching the necklace.
The film ends with Sylvie narrating that she still loves and misses "her," following the parallel between Ivy and Georgie.
Who is Sylvie's mother?
Georgie