As this series opens school girl Yoon Ji-woo is hassled by the police and bullied by schoolmates because her estranged father is working in a major drug dealing operation. On her birthday he returns home but is gunned down in front of her by an unidentifiably assassin. Determined to find and kill the man responsible she approaches the only person who might help; her father's associate, crime boss Choi Moo-jin. He takes her in and she trains in martial arts in the gang's training school; here she does well but makes an enemy of a fellow student. Choi Moo-jin has her declared dead then, under a new name, she enters the police as a spy. He gives her a clue to the identity of the killer; a discarded police issue pistol. As the years progress she advances and ultimately gets assigned to the drug squad. This gets her closer to the suspected killer; it also puts her in the investigation into Choi Moo-jin's activities and face to face with somebody who might expose her true identity.
I really enjoyed this South Korean series. The plot and general feel were more movie like than televisual... perhaps this is because key plot elements reminded me of the Hong Kong 'Infernal Affairs' trilogy. The story delivers plenty of impressive, sometimes bone-crunching, action as well as twists and turns to keep the viewer guessing as to the identity of the killer. Our protagonist gets into many scrapes and there is a real sense of danger; she certainly isn't immune to injury. The cast does a really fine job; especially Han So-hee who excels as Ji-woo. She manages to make scenes of a diminutive woman defeating several men believable. I liked the fact that the series is morally ambiguous; most viewers will be highly sympathetic to Ji-woo even though she is part of a criminal gang; even her boss is sympathetic to a degree... of course it helps that we are invited to suspect certain members of the police and there is a more unpleasant gangster to treat as a main villain. Overall I'd definitely recommend this to fans of the genre; it is top notch.
These comments are based on watching the series in Korean with English subtitles.