Ellie Christianson Julia Stiles is a fourteen-year-old girl living in an affluent neighborhood with her parents, Karen Christianson Chelsea Field and Ben Christianson William R. Moses, along with her younger sister Inger Christianson Vanessa Zima. Beneath their polished exterior lies a household tangled in dysfunction and secrecy. Ben is a workaholic whose hectic schedule keeps him away from home, and he is secretly involved with Lena Anderson Louise Myrback, the family’s housekeeper. Karen, meanwhile, pursues an illicit relationship with their next‑door neighbor, Lawson Smith Patrick Muldoon, as she schemes to leave Ben and take the girls with her. She fires Lena as a calculating step to start her getaway, unaware that Ellie has quietly witnessed one of Karen’s liaisons.
Tensions simmer at home as Ellie’s loyalty to her mother collides with Qthearing household drama. After a heated confrontation sparked by Ellie disobeying a school rule about makeup, Karen is found dead—brutally bludgeoned—turning the family’s life upside down. In the wake of Karen’s death, Ellie begins to assume some of Karen’s domestic duties for Ben and finds herself drawn into a troubling, unhealthy bond with him. The house becomes a pressure cooker where grief, jealousy, and desire mix with fear.
Lena’s desire for a green card brings her relationship with Ben into the open, and the two ultimately marry. This impromptu union stirs jealousy in Ellie, who has long harbored a desire to be his wife. Detective Boland [Michael Parks] begins to piece together Karen’s murder, which is soon ruled an act of homicide, with Ellie placed under suspicion as the prime subject of the inquiry.
During Lawson’s wedding celebration, Ellie ends up intoxicated and is found by Lawson, who takes her to his house, washes her hair, and lets her sleep. They talk about running away together, but Ellie wakes to the sound of a police officer at Lawson’s door, saying he’ll return with a warrant. They agree to meet again at 8 a.m. the following day.
Meanwhile, Inger discovers the weapon that killed their mother in Ellie’s closet—a drama mask—and swaps it back, masking the truth for the moment. Ellie returns to the house, avoiding questions about her whereabouts, while Lena urges Ben to discipline his daughter. When the father confronts her, Ellie pushes him to break things off with Lena, asserting her own claim over the family’s fragile balance.
The next morning, Ellie refuses to attend school, and Inger drops a hint about Ellie’s guilt as she prepares to leave for class. Ellie begins packing to meet Lawson, but a sudden crash downstairs spooks her. An unseen assailant strikes and kills Ellie in the same brutal fashion as their mother, leaving Lawson to arrive at the scene in tears and carry her lifeless body. Detective Boland arrives and shoots Lawson in the back, and the police quickly conclude that Lawson was responsible for the killings. Ben and Inger relocate to Lena’s apartment in the aftermath, while Lena notices Inger’s backpack and discovers the blood-streaked mask that killed Ellie hidden inside. The final shots linger on Inger’s cold, calculating gaze as she looks back at Lena, suggesting that Lena may now be her next target.
