Secretly, Greatly

As a North Korean top-class agent, Ryu-hwan infiltrates into the South and assumes the role of a village idiot in a rural town. He observes the townsfolk and waits patiently for his mission. One day, after 2 years of playing the role of the village idiot, fellow elite spies Hae-rang, posed as a rock star and Hae-jin, posed as an ordinary high school student, are dispatched to the same town as Ryu-hwan. He helps the other two spies settle in and teach them how to adjust in the South. They get used to the life in the South alongside the village people, still waiting for the grand mission. With the drastic power shift in the North government, the three spies finally receive the mission, but it's nothing that they've been waiting for. Can they accomplish the mission and go back home as legend?