Julie and Julia are twin sisters, both attached by the stomach. Julie is very sweet, caring and protective of Julia, although Julia has a harsh and cold nature. The girls promised each other to be together until they died.
While they are staying in a hospital, Julie and Julia meet a boy named Andy. The girls display mutual affection for him, but Andy only returns to Julie, much to Julia's jealousy. After recovering from an illness, Andy decides he wants to see Pim one last time and goes to the twins' room. As much as Julie wants to see Andy, Julia refuses to get out of bed and succumbs to jealous rage. Andy gets upset and leaves. Angry and in tears, Julie demands that she and Julia separate. To do this, the twins undergo a surgery, from which Julia does not survive. Julie fills herself with guilt thinking that if she didn't want to have the operation, Julia would still be alive.
Years later, Julie is married to Andy, and the couple lives in Toronto. He gets a call from USA that his mother has suffered a stroke. When Julie and Andy return to the USA, Julia's ghost comes back to haunt her. At first, Andy becomes very worried and starts demanding mental support for Julie. But even after the psychiatrist meets Julie, she still experiences a variety of ghosts by Julia. Julie listens to her breath on her side as she sleeps, as if she and Julia were still inseparable. She looks at Julia in the mirror instead of herself. On the elevator, she sees Julia resting her head on his shoulder. When she tries to relax in the bathtub, she is suddenly overboarded by Julia's ghost. When the lights go out, he sees a terrifying form of Julia. Ghosts follow Julie and she feels even more guilty. Later though, Julia's spirit also haunts Andy.
One night, Andy goes to see Julie's mother who reveals that Julie is actually Julia. His mother reveals that, after Julie demands to be separated, Julia strangles Julie out of jealousy. But when Julie dies, Julia suddenly breaks out of her anger and is shocked at her actions. She screams for help from her mother, who is devastated by Julie's death and never speaks to Julia again. To save Julia's life, doctors had to separate Julie's body from Julia's body. Julia assumes Julie's identity to be with Andy. This meant that all these years, Julia had been lying to Andy and it was actually Julie's ghost that was haunting her and Andy. Julia's mother was also fully aware of his actions, but remained silent. Later, it is shown that Julia killed her mother by cutting off the oxygen pipe so that she could not tell the truth to Andy. Julia had no idea that her mother had already told Andy the truth.
Andy confronts Julia, and in a moment of guilt, she tells the truth to Andy. Andy is disappointed and shocked by Julia's actions and decides to leave, but Julia knocks him unconscious and takes Andy hostage. However, Andy runs away, and the ensuing fight with Julia causes the house to catch fire. Andy throws a shelf at Julia and runs away. Trapped below, Julie's ghost confronts and puts Julia down, and as the burning debris pours around them, Julie smiles and Julia dies.
Andy visits the twin sisters' graves, and retrieves Julie's necklace that he gave her as a gift while they were in the hospital. He places it on their tombstone.
