Two North Korean soldiers are killed in the
Joint Security Area at a Northern guard house just across the
Bridge of No Return. Sergeant Lee Soo-hyeok, a wounded South Korean soldier on border duties, flees back to the South and is picked up by Southern troops, while the two sides briefly exchange fire. Two days later, in an attempt to ease tensions between the two Koreas,
Swiss Army Major Sophie E. Jean arrives to conduct a special investigation into the incident on behalf of the
Neutral Nations Supervisory Commission. While Soo-hyeok has confessed to the shootings, Sophie suspects something is amiss due to contradicting accounts of the events. Soo-hyeok states he was kidnapped and taken to the Northern guard house and, upon secretly freeing himself, shot three North Korean soldiers, leaving two dead. The North Korean survivor Sergeant Oh Kyeong-pil tells Sophie that Soo-hyeok barged into the guard house and shot everyone before retreating when the wounded Kyeong-pil returned fire. Autopsy reports show that one North Korean soldier, Jeong Woo-jin, was shot eight times, suggesting a grudge; additionally, a single bullet is not accounted for. Over the course of the investigation, witness Private First Class Nam Sung-shik attempts suicide by jumping out of the window of the interrogation room. A strange emotional reaction between Kyeong-pil and Soo-hyeok during a meeting causes Sophie to confirm her suspicions that the surviving soldiers and Woo-jin held a mutual friendship and were attempting to protect one another. Through flashbacks, it is shown that Soo-hyeok had been separated from a patrol in the North Korean side and partially tripped a mine. He is found and rescued by Kyeong-pil and Woo-jin. Over the next few weeks, the soldiers maintain contact by throwing written messages across the Bridge of No Return. Soo-hyeok is eventually invited to the Northern side and the three become a group of friends that soon includes Sung-shik, with the four agreeing to leave politics out of their friendship to remain loyal to their own countries. As tensions rise between the North and South, Soo-hyeok and Sung-shik return to the Northern guard house one night to say goodbye and celebrate Woo-jin's birthday, only to be discovered by a commanding officer from the North. A panicked Woo-jin betrays his friends, resulting in a
Mexican standoff. Kyeong-pil convinces all sides to lower their weapons, only for Sung-shik to panic and shoot the commanding officer when he reaches for his radio. When Woo-jin draws his gun again, Sung-shik shoots him and, in a daze, shoots his corpse several times. Kyeong-pil slaps Sung-shik out of his daze, takes the gun from him, and kills the still-alive officer. He then persuades Soo-hyeok and Sung-shik to come up with a false alibi of being kidnapped, before throwing away the evidence that he and Woo-jin were fraternizing with Southern soldiers. Soo-hyeok shoots Kyeong-pil in the shoulder to complete the alibi. While Sung-shik flees back across the border unseen, Soo-hyeok lags behind due to a wound sustained in the firefight and as such, he is the only soldier seen and picked up by the Southern troops. Back in the present, Sophie is eventually removed from the case when it's discovered that her father was a former North Korean general, thus technically rendering her non-neutral. Before leaving, she reaches out first to Kyeong-pil and then to Soo-hyeok in an attempt to learn the truth of the incident. She gives Soo-hyeok a lighter he first gifted to Kyeong-pil, which the latter now gives back. She reveals that Kyeong-pil in fact saw Soo-hyeok shooting Woo-jin first during the chaos before Sung-shik shot him. On his way out, a guilt-ridden Soo-hyeok snatches an officer's pistol and commits suicide. The film concludes with an American tourist's photograph of the Joint Security Area that accidentally contains all four soldiers prior to the incident. == Cast ==