Su-Na (Ko Eun-Ah), once a bright and adorable girl, locks herself alone in her room after her best friend's suicide. She starts to talk and behave as if someone else exists in her room, but never opens the door to anyone. Finally, her uncle brings his fiance, Yoon-Mi (Chae Min-Seo), a psychologist specializing with hikikomori (people who isolate themselves from society). Yoon-Mi soon discovers that Su-Na's troubles deal with the family's secret history.
