Plot
The eerie-sounding boiler room in the cellar of Sungwon Women's high school is the favorite hangout place of Yeong-uhn and her best friend Seon-min. Seon-min is a lively girl who has succeeded in becoming the top DJ at school. Yeong-uhn, on the other hand, is too quiet to be noticeable, except for her excellent singing. One late night, as Yeong-uhn practices singing in an empty music room at school, a strange voice suddenly starts blending with hers in harmony, carrying through the air of the whole building. On that same night, Yeong-uhn is murdered. The next morning, Seon-min notices that Yeong-uhn's seat is empty. Later, while playing in a room alone at lunch time, she hears Young-uhn's desperate voice calling to her. But she can't see anybody but herself in that small room she happens to be playing in! Shocked at hearing Young-uhn's voice without being able to see her, Seon-min passes out. Hearing the voice of her dead friend terrifies Seon-min, but at the same time she doesn't want to reject the possibility of staying in contact with her. Searching throughout the school, including in front of the elevator where her friend's body was discovered, Seon-min can't find any traces of Yeong-uhn. Seon-min suspects music teacher Hee-yeon, who used to pay unusual attention to Yeong-uhn, could have killed her friend. Later that night, following the voice of Young-uhn, Seon-min revisits the music room. In the darkness, Seon-min searches for her friend, and screams upon discovering th
