For Shion, an elite student in the technologically sophisticated city No. 6, life is carefully choreographed: school, study, and the occasional visit with his friend and classmate Safu.
One fateful day, however, he takes a misstep, sheltering an injured boy his age from a typhoon. Known only as Rat, this boy is a VC - a fugitive living outside the computerized tapestry of city control - and helping him will throw Shio's life into chaos and start him down a path to discovering the appalling secrets behind the superficial perfection of No. 6.