Hong Gil-dong is the illegitimate son of a minister. He is very bright and smart, however was told that he could not accomplish anything in this world, due to his illegitimate status. Thus he grew up spending most of his time being lazy and causing trouble for the people around him. However, a local monk thinks he is destined to be much more, and has taught Gil-dong martial arts. As the series progresses, Gil-dong realizes the severity of the injustices of the ranked world, and starts to fight against these injustices, stealing from the rich and giving to the poor.

Heo Yi-nok is an upbeat, naive and carefree girl. At the beginning of the series, she arrives from China with her grandfather, who has raised her. She meets and befriends Gil-dong. Yi-nok has a past she is unaware of: she does not know her grandfather is not her blood-related grandfather, and that her real parents were murdered. She eventually develops feelings for Gil-dong, who reciprocates her feelings.

Lee Chang-hwi also has arrived in Korea from China at the beginning of the series. He seems cold and calculating, as he also has a dark past in which his older brother, the current king of Joseon, tried to murder him. Chang-hwi is planning a revolution, in which he tries to overthrow the king and takes his place as, he believes, the rightful king of Joseon. He coincidentally bumps into both Gil-dong and Yi-nok. Both Gil-dong and Yi-nok help Chang-hwi realize what it takes to become a good king. He forges an alliance with Gil-dong and develops feelings for Yi-nok.

As the question of rightful succession comes into play, Gil-dong and Yi-nok are forced to take sides, all the while having to deal with their own personal problems: their love, Gil-dong with his father issues, Yi-nok with her murdered parents and their revenge.