Jiso has ruled the Kingdom of Silla as regent since King Beopheung died, keeping her young son Sammaekjong hidden outside of the capital Seorabeol and safe from enemies and assassins. As Sammaekjong comes of age, nobles, citizens, officials and Sammaekjong himself have all grown impatient for her to cede power. However the powerful nobles that tried to usurp power in the Kingdom continue to eye the throne and Ji-so fears the consequences of her ceding it.
In order to break the power of the nobles, who have grown accustomed to their privileges under the bone rank system, Jiso plans to create a new elite, the Hwarang, that will cut across the existing power factions, and to bind them to Sammaekjong and the throne. As this new elite of male youths bond and grow they are unaware that within their number is their future king, Sammaekjong, and Kim Sun-woo, a commoner with a secret even he is not aware of.