After the North-South Joint Statement on July 4, 1972, reunification fervor briefly sweeps over the Korean Peninsula. The Korean Central Intelligence Agency is forced to prepare for what could soon be the first inter-Korean summit and they are worried about South Korean president Park Chung-hee's meeting with the reclusive and potentially dangerous North Korean leader Kim Il-sung. To prepare Park for this conference, they decide to stage an imaginary summit so that they can simulate every scenario and plan for all eventualities. So the KCIA looks for an unknown (and bad) actor to play the body double for Kim Il-sung.

Kim Sung-geun earns his living doing odd jobs for a theater company, occasionally playing a walk-on part, and waiting for his big break. He gets cast in a small role as The Fool in Shakespeare's King Lear, but he forgets his lines due to stage fright. Sung-geun not only ruins the show, but he feels shamed in front of his son Tae-sik, who was in the audience and thought his father was the greatest actor in the world.

Backstage, the devastated Sung-geun is approached by Professor Heo, who praises his performance and tells him to show up at a "special audition." At the audition, Sung-geun is confused when the casting directors all seem to be government scientists, and even when his performance goes terribly, he gets told that it's exactly what they were looking for. He and 11 other actors pass the first round, then they're put on a bus and taken to the basement of the KCIA building where they are stripped, dragged into separate rooms and tortured. Too dumb to lie to his interrogators, Sung-geun is the only one left and gets chosen for the job. For Sung-geun, this is the role of a lifetime, and he puts his heart and soul into the performance, determined to have his acting acknowledged and to impress his son.

But when the summit gets cancelled, Sung-geun cannot let go of his Kim Il-sung persona and continues to act like the North Korean leader. Frustrated at his father, the adult Tae-sik places Sung-geun in a nursing home and refuses to visit him for the next 20 years. But when Tae-sik gets in trouble with loan sharks in the 1990s, he is forced to reconnect with his estranged father, whose dilapidated home could solve his problem.