Shin So Yool

Set in the 1990s, the drama centers around a female high school student Shi Won, who idolizes boyband H.O.T, and her 5 high school friends in Busan. As the timeline moves back and forth between their past as 18-year-old high schoolers in 1997 and their present as 33-year-olds at their high school reunion dinner in 2012, where one couple will announce that they're getting married.

Early in his reign, King Se Jong accidentally causes the death of his in-laws and their slaves in an attempt to save them from his brutal father, King Tae Jong. Two young slaves, Ddol Bok and his friend Dam, survive, but neither knows the other has. Ddol Bok blames the king and vows to kill him to avenge the deaths of everyone he loves. He spends several years becoming a great warrior. Dam, who has a photographic memory, becomes a court lady called So I, but she feels so guilty about her role in the other slaves' deaths that she is mute. Ddol Bok returns to the palace under the name of Kang Chae Yun in order to kill the king. However, he becomes embroiled in the mystery surrounding the deaths of several Hall of Worthies scholars. The deaths were caused by a secret society called "Hidden Root", which was created long ago by followers of Jung Do Jeon, with the goal of giving more power to ministers and less to the king. King Tae Jong killed Jung Do Jeon and all of his family except his nephew, Jung Gi Jun, who is now the leader of Hidden Root and lives in disguise not far from King Se Jong.