They're watching the border. Who's watching them?
Private Kang (Jang Dong-kun, A Warrior's Way) monitors a stretch of the South Korean coast lined with barbed-wire fencing. Driven by the belief that killing a spy is the highest honor, Kang eagerly awaits a chance to prove his worth as a soldier. One night, he mistakes a promiscuous couple for North Korean spies and shoots without hesitation. Despite receiving honors, he slowly begins to unravel under the grief of his actions. As he loses his grip on reality, tensions and paranoia escalate and further tragedy becomes unavoidable.