Maki and her son Takashi live together, but Takashi barely responds whenever Maki tries to talk to him. Feeling lonely, Maki spends her days in silence. One morning, they wake up in a room they don't recognize. The door is locked, and they have no idea how to open it. Panicking at being trapped, Takashi notices a note posted on the wall. It contains a disturbing message that shocks them both, and the story begins from there.