In the mid-1990s, an intelligence officer of South Korea's National Security Planning Department, codenamed "Black Star", disguised himself as a South Korean businessman to conduct business transactions with North Korea in order to infiltrate North Korean military units and gather intelligence on nuclear development. He had to win the trust of the enemy in the most dangerous places. Unexpectedly, he, who only wanted to complete his mission, unknowingly fell into a terrorist conspiracy between the top powers of North and South Korea.