At the same time as a mysterious incident, the state secret file disappeared. The only clue is Toya Modorihashi, a college student who was witnessed at the scene on the night of the incident.The "Special Investigation" department, commonly known as CIRO-S, was set up in the Cabinet Intelligence and Research Office in secret. Narabigaoka Tamako, a new investigator assigned here who deals with "unusual cases", decides to investigate the case and the file together with the cooperation of witness Toya.Despite Tamako's worries, Toya, who is deadly, approaches the core of the incident one after another in a way that no one can predict