The film follows Sylvie Cooper (Sara Gilbert), a shy, intelligent high school student from a wealthy family. She feels like an outsider both at school and at home. Her life takes a dramatic turn when she befriends Ivy (Drew Barrymore), a seductive, street-smart teenager from a troubled background.

Ivy quickly ingratiates herself into Sylvie’s life and family, charming Sylvie’s sickly mother Georgie (Cheryl Ladd) and developing a dangerous obsession with Sylvie’s father Darryl (Tom Skerritt). As Ivy grows more manipulative and entwined in the Coopers' lives, her intentions become increasingly sinister.