Secretly, Greatly is a 2013 South Korean action and comedy-drama film starring Kim Soo-hyun, Park Ki-woong and Lee Hyun-woo, who play North Korean spies who infiltrate South Korea as a village idiot, a rock musician and a high school student, respectively. They assimilate small-town life, pending orders, until one day, due to a sudden shift in energy in the North, their mission turns out to be an order to commit suicide. The film is based on the 2010 Covertness webtoon by Hun, which received more than 40 million hits on the page.
A group of spies called 5446 Corps have been trained by the elite of North Korea's special forces since their youth, apparently towards Korea's sublime goal of being unifying. They are ambitiously sent to South Korea, where each one disguises himself as a fool, an aspiring singer and a high school student. Passing the boring time without taking orders from the North, they gradually get used to life as ordinary neighbors in a small town, until one day, their mundane lives are turned upside down when a "secret and big" mission is suddenly attributed to them. Due to the events of the Second Battle of Yeonpyeong, South Korea requires the names, location and classification of 30 North Korean spies active in South Korea, promising to financially assist the North in the condition of Pyongyang for its spies' turns. To prevent the elites from falling into the hands of enemies, the North Korean government orders ten dozen active spies to take their own lives. Meanwhile, his North Korean army instructor Kim Tae-won crosses the border to eliminate those who refuse to follow.