The drama tells the story of royal secret agents in the Joseon Dynasty. They are the eyes and ears of the king, the mouth of the people, and the hidden heroes who guard justice. Kim Myung-soo plays a royal secret agent who works in the library during the day and transforms into a roaming swindler at night. He entered the palace after placing first in the state examination but is keener on martial arts. Kwon Na-ra plays a smart and beautiful Gisaeng who has no less courage than any man. Lee Tae-hwan plays a thief who, despite his fierce appearance, saves people from harm and later joins his brother in the secret inspection works....