The tragic chain of events begins when 13-year-old Cecilia survives a suicide attempt by slitting her wrists.

Despite a doctor's recommendation for more social interaction, the girls' religious mother and math-teacher father tighten their control. Cecilia eventually dies by jumping from her bedroom window.

After Lux (played by Kirsten Dunst) breaks a strict curfew following prom night, the parents lock the remaining girls inside their home indefinitely. Feeling suffocated and hopeless, the sisters eventually orchestrate a final pact to take their own lives.