Nao Tsunoda, sixteen years old, has moved to the Grauenheim apartment complex in Tokyo to live independently. One day she discovers her neighbor Erica Shimizu's headless corpse on the roof. In the neighbor's apartment: opera music playing, and Erica's severed head hanging from the ceiling, connected through a hose to a gas pipe so that it produces sounds matching the music. The murders continue — more residents of Grauenheim are killed, each corpse disfigured in a way that carries a specific symbolic meaning. Nao must decode the symbolism and identify the killer before becoming the next victim.