There is a special department in the Korean police system - the surveillance class, which consists of a group of detectives who are not amazing in appearance but have superb analytical and tracking skills. Under the command of squad leader Huang Shangzhong (played by Xue Jingqiu), the surveillance class has captured cunning criminals again and again and brought them to justice. One day, a passionate police officer Ha Yunzhu (played by Han Hyo-joo) passed the extremely harsh test of squad leader Huang with excellent results and became a member of the surveillance class, code-named "Flower Pig". Although he was a little green in his infancy, Huazhu quickly won the trust of the squad leader with his meticulous analytical ability. At the same time, a group of criminals led by James (played by Zheng Yusheng) are planning a secret operation against the stock exchange. Although the criminals have been found, James is extremely cunning and has superb anti-detection capabilities. A series of high-end cat-and-mouse games have been launched in the center of the downtown area...