When Interpol Hu Kai was investigating a serial murder case on campus, in order to get more clues, he chose to pretend to be a temporary substitute teacher at the school. During the investigation, Hu Kai was almost certain that the real murderer was a student in the class, but the student fled to other cities. Hu Kai believes that the arrest operation is much simpler than the detection. In fact, in every aspect, he has more advantages than a junior high school student. However, what he didn't expect was that all the seemingly favorable conditions eventually became shackles that restricted Hu Kai himself. He began to realize that he had actually been trapped in the chess game designed by this student from the beginning. Because for Hu Kai, the law itself is his rule and justice is his route, so as a chess piece, every move he makes has been seen through by his opponents...