Shin Soora lives cloistered in her apartment due to illness. Everything she does is online, which turns her into a really lonely young adult. None of the other neighbors can really understand her, and most end up treating her like a weirdo. Except for Kim Seokjin, from the 401, who is in fact her therapist, and Jung Hoseok, from the 402, who helps her with everything he can, being her only "real" friend since she moved in. But things start to take a turn and an unwanted change revolves in Hoseok's life when Min Yoongi moves to the apartment next to Soora's.