Tianshu You (played by Higashiyama Noriyuki), the patrol chief working at the lost and found office, has no chance to go to the scene at all. Most of the time, he deals with various lost items. Occasionally, he is annoyed when he receives elementary school students who come to visit. However, this does not mean that he is an incompetent and insignificant policeman. His keen observation and reasoning ability of details prove that his long-dormant police soul has not yet aged. One day, after assisting the on-site police to solve a housewife's suicide case, he was summoned by Kataoka Masatoshi (played by Yoshida Kotaro), the head of the 12th Department of the Metropolitan Police Department's Investigation Division. Although it is the Investigation Division, the 12th Department seems to be an unwelcome marginal place. Capable and ambitious criminal police have left one after another. Now there are only criminal police with strong personalities and little motivation, such as Samura Kosuke (played by Takashima Masahiro), Yamashita Takumi (played by Kataoka Ainosuke), Nagase Keita (played by Suzuki Hiroshi), and Mizuta Tamaki (played by Kurashina Kana). Tianshu's arrival seems to have finally changed the embarrassing situation of the 12th Department...