Geom is the son of virtuous nobleman Lee Won Ho, a trustworthy supporter and brother to the king and a central member of the secret organization Cheonwoohoe, comprised of important nobles, with the king as their leader. He lives peacefully in a plum-tree-surrounded house with his wife, daughter, and son. However, a mysterious rumor is spread that he is plotting to overthrow the king. Knowing about this, the king kills Lee Won Ho as he believes that 'two suns cannot exist in the same sky'. Geom witnesses the incident from the inside of a safe where his father hid him.
Later, he is saved and adopted by a retired thief, Seo Dol, after he becomes stricken with amnesia from the shock of losing his father and being forced to throw a rock at his mother's head to prove that he wasn't her son. 13 years later, Geom--now renamed Ryung by Seo Dol--starts to regain his memory and begins to search for his older sister Yeon--only to see her being sentenced and hanged.
Geom seeks revenge; with the emblem on the killer's sword he remembers from 13 years ago his only clue, he swears that he will find the one who killed his father and murdered his older sister. To find the sword and its owner, he disguises himself as Iljimae and breaks into the nobles' estates. During the course of his actions, he winds up fighting not only for himself, but also for the common people, although at the core his desire to bring the person who ruined his family to justice burns bright.