Su-mi was very close to her sister Su-yeon and her mother, who was currently dying from an unnamed illness. The mother's nurse Eun-joo secretly marries Moo-hyeon (the girls' father) which has caused tensions between them. One morning, the tensions have escalated in the dining room which causes both Su-mi and Su-yeon to leave.
Su-yeon enters her bedroom alone as she cries in her bed but fortunately, her biological mother is there to comfort her. As Su-yeon finally calms down and falls asleep, her mother hangs herself in the closet which causes Su-yeon to panick and she attempts to revive her mother to no avail as the closet suddenly falls ontop of her.
The rest of the family downstairs hear a loud crash and Eun-joo is the only one to investigate the source of the noise. Once she enters the bedroom, she is startled to see Su-yeon's hand scratching on the floor for help. Due to the tensions, Eun-joo leaves but ultimately changes her mind to save her but at the same time, Su-mi enters the room.
After Su-mi confronts her stepmother for ruining the family, Eun-joo holds her arm tightly and says in a bitter voice that she will "someday regret this". Confused, Su-mi leaves the room unaware that her sister is slowly being crushed to death by the closet that has fell ontop of her.
Several months after the incident, Su-mi has been institutionalised in a mental hospital (this happens in the beginning of the movie) as she developed psychosis and multiple personality disorder after becoming regretful and depressed over her sister's untimely death. One of the doctors question her about what caused her to be institutionalised but Su-mi remains silent until the doctor shows her a photograph of her family before Su-yeon's death.
Finally, Su-mi is released and her father drives her home but her mental disorder deteriorates as she hallucinates her sister and stepmother (throughout most of the movie, the stepmother is actually absent) being in the house. Along with the deterioration of her mental disorder, her house has been haunted by the vengeful ghosts of her sister and her biological mother. Su-mi imagines that her sister is there with her while she takes the role of her stepmother being "abusive and violent towards them". She even further acts out the role of her supposedly evil stepmother by breaking the neck of one of the family's birds.
Most of the confrontations between Su-mi and her stepmother were actually Su-mi harming herself to pretend that she is attacking someone. As this escalates, her father and her real stepmother finally arrive to calm her down and they send her back to the mental hospital.
The real stepmother finally gets a taste of her own medicine as the ghost of the biological mother crawls out of the same bedroom closet in which she died in and the ghost mysteriously kills Eun-joo. After the incident, it cuts back to Su-mi in the mental hospital, who is smiling at herself and calls Su-yeon's name gently several times.
The movie ends with Su-mi finally remembering the events that led her to be admitted in the mental hospital in the first place.
- She served as an inspiration for the character Anna Ivers from The Uninvited.