Although she only has an uncle and a grandmother in her family, seventeen-year-old Soo-na (KO Eun-a) grew up well, having everything she ever needed. Then one day, after the death of her best friend, she locks her bedroom door and turns into a Hikikomori. Confined in her room, she starts doing horrific things like talking to an unexplainable being and trying to commit suicide in front of her family. With Soo-na’s threats, her family gets more and more anxious and worried. Her uncle Se-jin’s (JUNG Yoo-seok) girlfriend and ‘Hikikomori’ expert, Yoon-mi (CHAE Min-seo) thinks there must be a dark family secret behind Soo-na’s strange actions and starts digging for answers.