A stunning historical epic chronicling the life of one of Korea's greatest rulers, Yi San tells the story of King Jeongjo, or Yi San, the 22nd ruler of the Joseon Dynasty, who is revered in Korean history for his championing of democratic rights for the common man and for his bureaucratic reform. Lee Seo Jin stars in a compelling performance as a king whose natural leadership ability and charismatic presence allow him to become one of Korea's most popular rulers and unite the land during one of the most tumultuous times in the Joseon Era. The story begins when Yi San, a young boy, manages to save his father's life when his father is suspected of treason by the current King, his grandfather. Protecting his father with the help of two friends, Song Yeon and Dae Su, Yi San cannot protect his two friends when their lives are put in danger by a later attempt on his own succession. After helping Yi San prove his innocence in an accusation of treason, Song Yeon's life is threatened, and she is forced to flee the capital with Dae Su. Yi San and Song Yeon do not meet again until years later when she returns to the palace as a damo with the art department. The drama traces Yi San's path through his rise to power, his assumption of the throne, and the constant intrigues and obstacles he surmounts.