The "Sweet Spy" extra chapter series tells the story of the four protagonists in the TV series: the ordinary police officer Lee Soon-ae, the head of the investigation section Jiang Jun, the mysterious Han Yu-il and Park Eun-joo before the first episode of the TV series. In this series, the author will explain some things that are not clearly explained in the TV series (such as how Jiang Jun met Lee Soon-ae and Park Eun-joo, Han You-il's childhood) with his own pen and his own style.