Girl Discovers A Mysterious Bag That Drastically Changes Her Life

The opening scene takes place in a mental institution where a teenage girl named Sumi is undergoing treatment for shock and psychosis. The doctor tries to communicate with her using family photographs, but Sumi remains silent. The doctor asks about her experiences leading to her hospitalization, but Sumi doesn't respond.

The scene then shifts to a few days later when Sumi returns to her family's isolated countryside residence with her father, Muhyun, and her younger sister, Su Yan. Both sisters hesitate to enter the house because they dislike their stepmother, Yoon Zhu. Instead, they head down to the lake for some fresh air. After being summoned back to the house, they are greeted by Yoon Zhu's feigned welcome. However, the two sisters remain unresponsive and go upstairs to their room. Sumi starts unpacking and arranging her belongings but discovers an identical diary and clothes with the same design as hers. It seems like she's not allowed to wear anything else.

During dinner, the atmosphere remains quiet. Yoon Zhu announces that she has invited her brother and his wife to dinner the next day, but nobody seems interested. Sumi expresses her disapproval of dining with her stepmother's brother, and she leaves the dining table, followed by her sister. Sumi asks her sister to confide in her if their stepmother ever bothers her. Later, everyone goes to bed. Muhyun chooses to sleep on the living room sofa, highlighting the strained relationship between him and Yoon Zhu.

At midnight, Su Yan hears a strange noise and sees a hand extending into her room. She hides under her blanket, but it's slowly pulled away. The door suddenly slams shut, frightening her. She runs to Sumi's room for comfort. Sumi checks downstairs but only finds the television broadcasting static. She also finds her father asleep on the sofa and adjusts his blanket. Yoon Zhu appears from the shadows and tells Sumi not to disturb him. They argue, and Sumi leaves, comforting her sister with a hug. During the early hours, Sumi has a nightmarish vision involving her dead mother. Upon waking up, she sees a horrifying apparition of a long-haired woman crawling towards her. The ghostly figure starts to approach her, but Sumi snaps out of it.

Later, Sumi notices bloodstains on her bedding and her sister's shorts, indicating they're on their periods. To get sanitary pads, Sumi goes to her stepmother's room and discovers that Yoon Zhu is also menstruating. It's strange that all three women have synchronized cycles. The sisters whistle their biological mother's favorite melody on the balcony, and their father advises them to come inside. Sumi suggests getting rid of Su Yan's wardrobe, but her father reminds her they agreed not to discuss it. Their relationship appears cold, marked by frequent disagreements. Sumi finds family photographs revealing that Yoon Zhu used to be an in-home nurse who cared for their terminally ill mother. She also discovers bruises on Su Yan's arm, but her sister refuses to answer her questions. That night, Yoon Zhu's brother and his wife join them for dinner. Yoon Zhu makes insensitive jokes, and Mih suddenly collapses and convulses. Muhyun and Sumi rush to her aid, and she eventually recovers and leaves.

Back at home, Yoon Zhu notices the sink door opening on its own and investigates beneath it but finds nothing. Unbeknownst to her, a girl with long hair is seated at the dining table. She senses an eerie presence, and a ghostly hand grabs her arm. She hastily retreats, then finds herself face to face with the girl from the dining table. Yoon Zhu confides in her husband about strange occurrences in the house since Sumi's return, but he doesn't believe her. Later, he finds Yoon Zhu's pet bird killed in its cage. Yoon Zhu confronts Su Yan about torn pictures and assaults her, locking her in the closet. Sumi hears her sister's screams, unlocks the closet, and apologizes for not hearing her cries sooner. Their father arrives and learns of the mistreatment.Sumi questions Yoon Zhu about the injuries, and a violent altercation ensues. Yoon Zhu attempts to harm Sumi with a garden statue but is interrupted by Muhyun. Sumi is injured but saved.

Later, Yoon Zhu takes medication, and Muhyun asks her to control her violent behavior. Yoon Zhu spots a hair clip on the floor, and a ghostly hand grabs her arm, but she escapes.

Muhyun makes a grim discovery – Yoon Zhu's pet bird is dead. Yoon Zhu finds torn pictures with her face scratched out and believes the girls did it. She assaults Su Yan, and Sumi intervenes. Sumi and her father take Yoon Zhu back to the mental institution. Yoon Zhu promises to visit Sumi often. However, Sumi remains silent.

In the evening, Yoon Zhu hears footsteps from Su Yan's old room and investigates. She encounters a ghostly figure and is ultimately killed. In the hospital, Sumi appears at peace.

The story then flashes back to when the children's mother was alive. Muhyun had an affair with Yoon Zhu, their in-home nurse, which led to their mother's demise. When Su Yan found her mother dead, she was crushed by a collapsing closet. Sumi was traumatized, leading to her mental health issues.

It's revealed that Sumi suffered from dissociative identity disorder, leading her to perceive her stepmother as an enemy. She hates her stepmother deeply, which influenced her perception of events. The events involving Yoon Zhu's sister's seizure on the floor were part of Sumi's delusion.

The stepmother's portrayal in the earlier scenes was a creation of Sumi's imagination. The father and Sumi discover that Su Yan died long ago. Sumi takes medication to stabilize her emotions. Her father and the real Yoon Zhu take her back to the mental institution.In a later scene, Yoon Zhu encounters a ghostly figure in her home and is killed.

The story concludes with the revelation that Sumi's trauma and mental illness were a result of her mother's death and her father's affair with Yoon Zhu.