The plot begins when Ju-young’s sister, Ju-hee, inexplicably disappears from their apartment. As Ju-young investigates, she starts to hear strange sounds—sounds that her hearing aids would normally filter out. This leads her to believe that a malevolent presence is haunting the building and may be responsible for her sister’s disappearance. The film is praised for its sound design, which is used to create a claustrophobic and terrifying atmosphere.