Once upon a time in Korea, a young female detective Namsoon (Ji-won Ha ) and her trusty companion Detective Ahn (Sung-kee Ahn) are called to investigate a case involving counterfeit money. She goes undercover and disguises herself in several incarnations in order to track the criminals. Namsoon repeatedly encounters a mysterious, handsome swordsman named Sad Eyes (Dong-won Kang) - and it is sparring at first sight.

Evidently and inexplicably attracted to each other, the fiery Namsoon and the enigmatic Sad Eyes engage in a cat-and-mouse game and in beautifully choreographed duels that only strengthen their mutual feelings. But their combat also results in the devastating disclosure that Sad Eyes, as a loyal acolyte of the Minister of Defence (Song Young-chang), has a role in the latter's plot to seize control of the country and is therefore Namsoon's enemy.