In the late 18th century, because of a dream, King Yeong Jo locks his son, Crown Prince Sa Do, into a rice storage chest without water and food. Sa Do's son, Prince San, tries to carry food for his father. He meets with Seong Song Yeon and Park Dae Su, and they help San, but the children don't know who is he in fact -- he wears eunuch's uniform and says he is Mu Duk, an inferior of Prince San. They become friends that night. Song Yeon and Dae Su help their friend and save him many times from death.