In 1987, Ivan and Catherine Greer (Michael Des Barres and Merete Van Kamp) live with their 9-year-old daughter Joy, their housekeeper Rebecca (Athena Massey), and her two daughters, Ivy, age 9, and Violet, age 8. The three young girls live as sisters, but the more rambunctious Ivy is bored by their childish games of tea parties and rejoices at Ivan's unexpected early day return from the office, saying, "There's going to be fireworks."
Ivy's prediction soon comes true. Ivan catches Rebecca in bed, having sex with the handsome pool boy, and the two men scuffle. As Ivan tends to his wounds, he and Rebecca begin a loud argument about her adulterous affair and why Rebecca cheated on him. The shouting brings Catherine's attention from the garden. Upon learning of the affair, she immediately evicts Rebecca and her children. Rebecca retaliates that Catherine cannot fulfill Ivan's sexual desires like she could. As Rebecca and her daughters leave the Greer mansion, Joy is heartbroken to lose her only known siblings.
Ten years later. Violet (Jaime Pressly as a teenager) returns to the Greer home and is reunited with Joy (Megan Edwards as a teenager) for the first time in ten years. Violet states that she is looking for a summer time residence while working as a waitress at Denny's Restaurants and planning to attend the local Junior College. Joy suggests that she reside with them and stay in the late Catherine's room. Joy tells Violet that her mother died a few years ago from cancer, and Violet relates to that explaining that her own mother, Rebecca, also died from cancer and her sister, Ivy, also is dead which Violet refuses to talk about. Joy is an amateur tennis star and engaged to her Princeton boyfriend, Michael (Greg Vaughan), who will be working as an intern for Mr. Greer's bank.
During a late night party, Violet feels isolated and ridiculed by Joy's Ivy League friends, and excuses herself for late shift work. Afterward, Michael takes Joy to her room and initiates foreplay, only to be rejected. He accuses Joy of being sexually frigid, and insultingly says he understands her father's infidelity. As Michael is on his way out, he runs into Violet returning, who is dressed in a black-leather sadomasochistic costume, which causes him to question her employment at Denny's. Violet states that the two have gotten off on the wrong foot, and proceeds to perform oral sex on him.
Over the next few days, Violet's obsession with Joy motivates her to destroy all of her other relationships so she can have Joy as her one and only friend. When her tennis partner Jaimie (Shanna Moakler) comes over to practice with Joy, Violet spikes their drinks with alcohol causing both Joy and Jaimie to pass out on the tennis court. Violet drags Joy to her bed, and drags Jaimie to her bed where she undresses her, and then undresses herself into her bra and panties and lays in bed with the unconscious and handcuffed Jaimie, convincing her that they have just engaged in a sexual threesome. A horrified, half clothed, and handcuffed Jaimie flees the Greer house, thus never to return.
Michael is Violet's next target. While by the Greer pool, she convinces him Joy has been unfaithful and seduces him into sex, while she provides him with cocaine to reignite his former addiction. Michael is not appreciative of her vices and vows never to see her again, thereby confirming Violet prejudiced belief that all men are uncaring and deceitful (in which Violet's unstable and nymphomaniac mother, Rebecca, apparently rasied her to belive).
Ivan is the next to be seduced as Violet sabotages his date when she swims topless in his pool, and dresses in his late wife's clothing. The two wish to rekindle the passion that existed during Ivan's affair with Rebecca.
The Greers' housekeeper, Mrs. B (Susan Tyrrell) (whom always suspected from the very start that Violet is not who she claims to be), quickly catches on to the recent events, and makes enemies with Violet in her attempts to thwart her schemes.
One day, Michael confronts Violet while she is "street walking". He then reveals to her that he has lost his internship at the bank because of drugs and that he knows of her schemes, including working as a sadomasochistic prostitute, her false employment at Denny's, and her dark family history including the death of Ivy (alluding to the original film). He threatens that she must leave the Greers' before he tells Joy the truth.
When Michael arrives at the Greers' later that day, Violet attacks him and murders him with a drug overdose. Later that day, Joy returns from a failed tennis match, distraught at the recent drama of events, only to learn of Michael's death and walk in on her father and Violet in sadomasochism. As a traumatized Joy flees the house, Ivan tells Violet she must leave, to which she accuses him of repeating the abandonment of her mother. She hides the drugs for Ivan's heart condition and places him in the garage fatally poisoning him with carbon monoxide by leaving a car engine running.
After a drive, Joy returns that same night, to now discover Mrs. B is also murdered. Violet induces Joy to dress up and play tea like they did when they were children, where they will commit suicide together by drinking poison. Joy violently resists by splashing the poison on Violet's face, and the two wrestle around the room. Violet attempts to stab Joy with a pair of scissors, but Joy is able to knock her back before she strikes. Joy races out of the room to the stairway, where she leans on the banister and cries out for help. Violet regains her senses and goes to resume her attack. Violet is spun around by Joy and begins to lose her balance at the top of the stairs. Joy grasps the end of Violet's pearl necklace to keep her from falling.
Still holding on to the pearl necklace, Joy pleads with Violet to reach out and save herself. Instead Violet leans her head back and raises her arms in the air... clearing wanting to fall. In doing so, the necklace shatters and Violet's feet slip, causing her to fall backwards down the stairs. Violet lies motionless at the bottom of the stairs... dead from a broken neck. Joy calmly exits the mansion and walks down the driveway to the street and walks away into the night. The loss of her entire family is clearly saddening to Joy, but it may provide her with the opportunity to begin anew, and leave behind the darkness of her family past.