Sylvie Cooper, portrayed by Sara Gilbert, is a disaffected and cynical teenager navigating life at a prestigious private school for the affluent. Her world shifts when she encounters "Ivy," played by Drew Barrymore, a rebellious yet perceptive girl from a less fortunate background, at a local hangout. The moment takes a dark turn when, as they witness a wounded dog, Ivy brutally ends its suffering by smashing its skull with a pipe, leaving Sylvie both shocked and intrigued.
Their connection deepens when Sylvie finds herself in the office after making a bomb threat to a local TV station, where her father, Tom Skerritt, works. Upon seeing Ivy again, they strike up a conversation that solidifies their budding friendship. When Ivy asks for a ride from Darryl, Sylvie's father, he hesitantly agrees, despite his initial reluctance. Ivy takes advantage of the situation, using the front seat to flirt with Darryl, showcasing her more provocative side.
Once Sylvie is free from grounding, she and Ivy reunite at their hangout. It’s during their walk to Sylvie's sprawling mansion that Sylvie reveals her complex family background and the profound scars from her past, including a failed suicide attempt. Upon arrival, Ivy expresses a morbid curiosity about death, stating that if she were to die, she would prefer to fall. Sylvie's sickly mother, Georgie, portrayed by Cheryl Ladd, interrupts them, and although initially skeptical about Ivy, she slowly comes to appreciate Ivy's vibrant spirit and even allows her into their home. Their bond grows stronger, leading to shared clothes and nights spent in the same bed.
As Ivy's influence permeates Sylvie's life, the daring friendship takes a wild turn with Ivy suggesting they both get tattoos to symbolize their sisterhood. Tension builds during a party hosted by Darryl to revive his sagging career, where Ivy cunningly finds a way to replace Sylvie at the charity center by manipulating the situation. At the party, Ivy transforms, donning expensive clothes from Georgie's wardrobe. An intimate dance between Ivy and Darryl leads to a catastrophic fallout when Georgie discovers them together. After Ivy drugged Georgie with champagne, a hidden animosity begins to surface.
Sylvie feels overshadowed and betrayed by Ivy, culminating in a dramatic confrontation where Ivy's obsession becomes evident. After a fateful night in the woods that leads to an unfathomable act of betrayal, Ivy pushes Sylvie's fragile mother from a balcony, staging it as a suicide. The tumultuous events escalate when Ivy drives them in Georgie's old sports car, hinting at sinister motives by humming a tune reminiscent of the past.
In a gripping climax, Sylvie gains consciousness in the hospital and races home to save her father from Ivy's treachery. However, upon her arrival, a chaotic storm mirrors her internal turmoil as she discovers Ivy and Darryl entwined. In a haze of rage and pain, Sylvie's hallucinations cloud her judgment, leading to a fateful confrontation on the balcony. The fight culminates in Ivy's tragic fall, severed from her life while clutching Sylvie's necklace.
In the end, through reflective narration, Sylvie reveals that her feelings remain conflicted. She holds onto a bittersweet memory of Ivy, acknowledging the deeper loneliness that haunted her friend. Sylvie's haunting conclusion echoes, “I forgive her because she was even more alone than me.”
