Nobody Knows tells the story of four siblings and their young mother who move into a small apartment in Tokyo. The film begins when the family is moving into a small rented apartment. Only the eldest, Akira is known to the landlord, while the youngest boy and girl, Shigeru and Yuki, hide in separate suitcases. The elder sister, Kyōko, comes separately by train. All the children have different fathers. They are not allowed to go to school or to be seen by others, and only Akira is allowed to go outside. Yet, the family seems to be happy.