A royal body double risks everything to save his beloved country from collapse in this historical rama set during Korea's Joseon Dynasty, and inspired by a mysterious 15-day gap in the country's history during one of its most turbulent eras. Korea is in chaos, and totalitarian King Gwanghae (Byung-hun Lee) fears that his life may be in danger. Determined to survive, he commands his counselor to recruit a stand-in to take his place in a worst-case scenario. The counselor soon returns with Ha-seon (again, Lee), a village performer and peasant who's a dead ringer for the tyrannical ruler. Later, when the king is poisoned and lapses into a coma, Ha-seon takes his place. Under orders from the king's chief advisor and chief eunuch, Ha-seon maintains the illusion despite constant threats of exposure and death. When the royal stand-in realizes that his country's future rests in his hands alone, however, the time comes to take drastic action no matter what the consequences.