Jae-Hyeok (Kim Nam-Gil) lives with his mother (Kim Young-Ae), his sister-in-law (Moon Jeong-Hee) and nephew Min-Jae (Bae Gang-Yoo) in a small Korean town. He is dating Yeon-Joo (Kim Joo-Hyun), while working at the local nuclear power plant. Meanwhile, Pyung-Sub (Jung Jin-Young) works at the same nuclear power plant. He is worried about conditions there, but nobody in the government listens to him. An earthquake strikes the small town where Jae-Hyeok lives and causes explosions at the nuclear power plant. The situation quickly spirals out of control, leading the entire nation to panic. To prevent another nuclear disaster, Jae-Hyeok and his co-workers return to the nuclear power plant.

Amid national chaos and fear for his life, tyrannical King Gwanghae orders his trusted councilor Heo Kyun to find a royal body double. He hires Ha-seon, a peasant mimic who bears a perfect resemblance to the King. When King Gwanghae collapses from a mysterious poison, Ha-seon reluctantly becomes a King. He must follow his conscience to save his country from collapse, avoid assassination, and pull off the biggest masquerade in history. K Written by CJ Entertainment