Young-eon, the top singer at an all-girls school, is murdered by a music sheet cutting her throat in the opening scene. The next day nobody can see or hear her except her friend Seon-min, who can only hear her. The two attempt to find out what happened to Young-eon. Seon-min begins speculating that the music teacher must have killed Young-eon. The mystery behind her death is slowly unraveled as Young-eon has flashbacks of life before her death. Seon-min befriends a strange and lonely girl at school named Cho-ah, who can hear the voices of the dead, and she helps the two solve the incident. Meanwhile, the music teacher kills herself. Seon-min begins to doubt what Young-eon says after Cho-ah tells her that ghosts only remember what they want to, meaning Young-eon's memory may be incorrect. Young-eon's body is found in on top of the elevator. Young-eon is running out of time to discover who the other ghost is; if her friend forgets about her, she will lose her voice. Some of the flashbacks include her mother, who is in a hospital. In one flashback, she talks to her mother about how she will learn to drive when she is old enough. Another features how her mother committed suicide by jumping off the top of the hospital. In the end, Young-eon is revealed to have driven her mother to suicide, and might have multiple personality disorder due to the trauma and guilt of encouraging her mother to kill herself. Young-eon brings tears to her music teacher's eyes when she asks the teacher to sing, leading the latter to contemplate suicide. It turns out that Young-eon had been hearing the voices of her teacher and of the ghost, Hyo-jung, the whole time. Young-eon wanted the teacher dead to get rid of Hyo-jung's voice. Hyo-jung was a student and top singer at the school who fell in love with the music teacher. She has the same voice as Young-eon and they are both recorded in a song. Hyo-jung is revealed to have shot the music sheet at Young-eon's throat in the opening scene out of anger at losing her voice. Seon-min thinks Young-eon should move on but Young-eon is angered by her statement, since she wants nothing more than to live again. Young-eon kills Cho-ah and takes over Seon-min's body. She then walks alongside Seon-min's mother, talking about how, as soon as she is old enough, she will learn to drive. A scene during the credits shows Cho-ah shouting in frustration, but voiceless.
