When high school student and aspiring singer Young-Eon (Ok-bin Kim) is murdered, her body disappears but her soul becomes trapped within the school, and only her best friend, Sun-min (Ji-hye Seo), can still hear her singing. Determined to find her friend's murderer, Sun-min's resolve is shaken when a music teacher and another student die on campus. Could Young-Eon have committed these horrific acts or is someone else lurking around for their next victim?