Secretly, Greatly
은밀하게 위대하게 (original)
As a North Korean sleeper cell agent, Ryu-han infiltrates 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 student, are dispatched to the same town as Ryu-han. He helps the other two spies settle in and teach them how to adjust in the South. There is a sudden drastic political power shift in the North and all three spies receive an urgent and ultimate mission.
Starring Kim Soo-hyun, Park Ki-woong, Lee Hyun-woo, Son Hyun-joo, Ko Chang-seok, Kim Sung-kyun, Shin Jung-geun, Hong Kyung-in, Lee Chae-young, Park Eun-bin
Watch "Secretly, Greatly" on Amazon released in 2013. It's a action and drama movie, and has a rating of 6.8 out of 10 from Imdb which is usually fine for this kind of movie, and is currently only available for purchase or rent.