Secretly, Greatly

A group of spies called the 5446 Corps were trained since their youth by North Korea to unify Korea. They are ambitiously dispatched to South Korea, where each disguises himself as a fool, an aspiring singer, and a high school student. Passing the time without receiving orders from the North, they gradually get used to life as ordinary neighbors in a small town. One day, their mundane lives are turned upside down when a "secret and great" mission is suddenly assigned to them.