The film follows three top North Korean spies who are assigned to be Deep Cover Agents in a South Korean village. Won Ryu-hwan (Kim Soo-hyun) is disguised as village idiot Bang Dong-gu, Rhee Hae-rang (Park Ki-woong) plays wannabe rockstar Kim Min-su, and Rhee Hae-jin (Lee Hyun-woo) plays a high school student. The three men settle into their mundane lives until power shifts between the North and South mean they are finally assigned a mission: to prevent them from falling into the South Korean governments' hands, they must take their own lives.
- Beneath the Mask: Underneath his simpleton persona, Ryu-hwan has a running commentary on how idiotic he thinks the South Korean villagers are.
- Clark Kent Outfit: Dong-gu looks like a twig while wearing his tracksuit. Underneath it, Ryu-hwan is totally jacked.
- Crouching Moron, Hidden Badass: Directly invoked by Ryu-hwan, whose cover is the village idiot Dong-gu. In reality, Ryu-hwan is one of North Korea's top spies, a Cunning Linguist who is incredibly adept at reading people.
- Cunning Linguist: One of Ryu-hwan's greatest assets as a spy is that he can speak five languages.
- Deep Cover Agent: North Korean spies are instructed to blend in in a South Korean village. Two years later Ryu-hwan's cover is still seamless.
- Downer Ending: Hae-rang and Hae-jin die in a shootout against North Korean special forces. Ryu-hwan is probably dead as well.note
- Dying Dream: After Ryu-hwan jumps off a roof with Hae-jin's bullet-ridden body, we get a flashback of the three spies cleaning anchovies back in the village. They discuss their wants and dreams in life.
- Kids Are Cruel: Dong-gu is introduced dodging rocks thrown at him by the village kids.
- Like a Son to Me: The ending reveals that the village granny Soon-im had grown to consider Dong-gu as her son, changing his wage marks in her bank book first to "our Dong-gu" then "My Second Son". Then it's revealed she had been setting money aside for his future wedding.
- Mood Whiplash: The first half of the film is more or less a lighthearted story that finds the humor in well-trained spies forced to live mundane lives. Then the suicide order comes, and the film becomes more of a dark action thriller.
- My Sister Is Off-Limits: Yoo Joon is introduced slapping Dong-gu for mooning after his sister Yoo Ran.
- Piggyback Cute: Dong-gu piggyback carries his "crush" of sorts Ran back to her place after she gets drunk and nearly throws up on him.
- Toilet Humor: Invoked, Ryu-hwan has a schedule for pissing and pooping in public to keep up his "village idiot" persona.
- Trapped Undercover: The three main characters are all North Korean spies living undercover in the South. They take on specific roles as a village idiot, pop star, and student, and eagerly await orders while they grow attached to unsuspecting people in their community. For much of the movie, no orders come, but near the end it's revealed that political upheaval has led to the cancellation of their program, and that their only order is to kill themselves. This leads to a climax with a three-way showdown between the protagonists, the South Korean spies, and their superiors.