A North Korean teen attempts to save his sister's life by volunteering to infiltrate South Korea, but finds his mission complicated after he rescues a teenage girl in the course of his trek, inadvertently exposing himself to his sworn enemy's intelligence agency and becoming the target of a ruthless hit man dispatched by his own government. When Myung-hoon's father fails to execute a crucial mission into South Korea, his son and young daughter Hye-in are locked away in a North Korean labor camp. Determined to save his sister at all costs, Myung-hoon attempts to prove his loyalty to the North by posing as a defector and attending high school in the South while clandestinely carrying out a crucial espionage mission. But he's exposed when, in a moment of compassion, he saves his classmate from certain death. When his heroics draw the attention of the South Korean government, Myung-hoon must complete his mission before he is captured and tried as a spy, or killed by the cold-blooded North Korean assassin who is hot on his trail.