Being the sister of upright police officer isnt an easy thing. Crime, Mystery and Thrill become a part of the daily routine which can be laborious over a point of time. But not for Park Hyejin. An energetic and intelligent girl, bubbling with life and enthusiasm to become a police officer just like her beloved elder brother. Being a college girl doesnot stop her from aiding her brother in his strenuous missions. She feels every case might lead her to the ultimate killer she has deen searching for; the one who killed her parents in a seeming accident. 

One such day, she becomes a part of a secret undercover mission that not only brings her closer to her destined one but also changes her life forever. 

P.S There is a pun on the word Mole in the title. It means a mark on the skin (we all know of) and a spy who gradually achieves an important position within the security defences of a country.