Set during the Silla dynasty, Sam Maekjong is the son of the fallen king and present queen regent, Jiso, but he has been kept in hiding for protection ever since he was a young boy, when his father was murdered. Over the years the powerful nobles have tried and failed to usurp power from Jiso, causing her to grow wary and later even reluctant to hand the throne over. As her son comes of age, she creates the Hwarang, an elite group of male youth who train in fighting and education. Their existence cuts across the existing power factions and Sam Maekjong is amidst their ranks under the false name Kim Ji-Dwi, unbeknownst to other Hwarang members.

During the confusing and conspiratorial Joseon Dynasty King Gwang-hae orders his councilor, HEO Kyun, to find him a double in order to avoid the constant threat of assassination. HEO Kyun finds Ha-sun, a jester who looks remarkably like the king, and just as feared, Gwang-hae is poisoned. HEO Kyun proposes Ha-sun fill the role as the king until Gwang-hae recovers fully and grooms Ha-sun to look and act every bit the king. While assuming the role of the king at his first official appearance, Ha-sun begins to ponder the intricacies of the problems debated in his court. Being fundamentally more humanitarian than Gwang-hae, Ha-sun’s affection and appreciation of even the most minor servants slowly changes morale in the castle for the better. However, his chief opposition, PARK, notices the sudden shift in the king’s behavior and starts to ask questions.