One day in the Joint Security Area at the Panmunjom border, a North Korean soldier (Shin Ha-kyun) at the sentry post was killed by an unknown bullet, triggering a gunfight between the two sides. The most suspected murderer is a South Korean soldier on the border, but the South Korean side accused North Korea of inciting the incident first, and both sides believed that the opponent should be responsible for this. In order to solve this headless case, the North and the South agreed to have a neutral country to investigate and coordinate. Sophie (Lee Young-ae), a Korean girl with Swiss nationality, was sent to investigate the incident. Lee Soo-hyuk (Lee Byung-hun) on the South Korean side remained silent, while the survivor Oh Kyung-pil (Song Kang-ho) on the North Korean side showed hostility, and things were confusing. As she got to know more, Sophie discovered that there was an inside story behind the incident, and there was someone else at the scene...