Secretly, Greatly

Secretly, Greatly is a 2013 South Korean action 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 to small-town life while awaiting their orders, until one day, due to a sudden power shift in the North, their mission turns out to be an order to commit suicide.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.

Poster © the film's rights holders.