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