When you killed your psycho boyfriend, Jeon Jungkook, you thought that you were safe from him now. You were walking in a new building that was under construction, you lost your necklace when you killed Jungkook in there and you loved it so much and decided to risk and go there at night when no one was around, but suddenly you heard the same whistle ( remember DNA song) after 2 years of his DEATH.