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 beloved uncle Jeong Se-jin (Jeong Yoo-seok) brings his fiance, Yun-mi (Chae Min-seo), a psychologist specializing in hikikomori (people who isolate themselves from society), and she finds Su-na's troubles lurk much deeper than the horror of the suicide.
