In January 1992, Major Park Seok-young finds himself at the center of a covert mission when he is recruited by the Agency for National Security Planning (ANSP). His objective? To delve deep into the secrets of North Korea's nuclear program, knowledge that only a select few, including its leader, Kim Jong Il, are privy to. Under the guidance of Director Choi, Park adopts the guise of a down-and-out businessman turned alcoholic, having fallen from military grace due to mounting debts. His primary task is to establish a rapport with Ri Myung-woon, the influential director of the North Korean External Economic Committee.
Positioned in Beijing, Park successfully crafts an image as a trader dealing in North Korean goods, which piques the interest of Ri and various North Korean officials. The plot thickens when the ANSP orchestrates a crackdown on counterfeit North Korean products originating from China, leading to the arrest of Jang Sung-hoon, the nephew of Jang Sung-taek. This event prompts Ri to seek connections with Park, hoping to secure funds for Jang's release. However, their interaction is tinged with suspicion as Ri demands assurance of South Korean intelligence before extending his trust.
To facilitate their dealings, Director Choi arranges for Park to deliver cash alongside confidential information, including imitation Rolex watches presented as gifts to the North Koreans. During a pivotal meeting, Jung Moo-taek from the State Security Department proposes a more direct relationship, offering Park the chance to sell military secrets. Park, feigning shock, declines this tempting but dangerous opportunity. Tensions continue to escalate during a dinner when Jung's mistrust leads to a scuffle, revealing the Rolex watches. Although Ri is dissatisfied with Jung's overzealous behavior, he ultimately chooses to trust Park.
As part of his cover, Park proposes an ambitious advertising project with Han Chang-joo, who aims to film locations in North Korea. This venture requires the nod from Kim Jong Il, and in the North, Park and Ri successfully persuade him, which also includes plans for a luxurious resort on Mount Geumgang and sourcing artifacts from historical dynasties.
Amidst the filming, Park seizes an opportunity to explore Yongbyon under the guise of artifact sourcing, drawing him closer to the sensitive nuclear facilities. It is here that Ri and Kim Myung-soo, a member of the Kim family, present Park with a symbolic pin of the Kims. However, as Park witnesses the dire conditions wrought by famine in North Korea, he learns that Kim is discontent with the regime's leadership, a sentiment that ultimately leads to Kim's exile.
With the rise of Kim Dae-jung bringing a wave of change that threatens the ANSP's power, Choi instructs Park to deliver a communiqué to the North. Feeling doubtful about his agency's intentions, Park discreetly wiretaps a meeting where Choi uncovers plans to attack South Korea’s outlying islands to undermine Kim’s reputation. Faced with a moral dilemma, Park confronts Choi, who mocks his alignment with communist ideals. Instead, Park aligns with Ri, who secretly shares his disillusionment with the regime.
Their path leads them to another meeting with Kim, where they dissuade him from further provocations after Park exposes Jung's embezzlement of US$400,000. The political landscape shifts dramatically with Kim Dae-jung's election as president, yet the ANSP reacts by revealing Park's true allegiance. In Pyongyang, Ri gives Park a devastating choice: defect to the North or face execution. Park refuses, but instead of sealing his fate, Ri helps him escape by providing a special visa. Their farewell is heartbreaking, as Ri remains behind, trusting in his survival against the regime's wrath. Meanwhile, Kim begins to investigate the ANSP's interference in the elections, leading to a reshuffling and the transformation of the agency into the National Intelligence Service.
Fast forward to 2005—after years separated by political turmoil, Park and Ri's fates intersect once more in Shanghai. This unexpected reunion occurs during a South Korean advertising campaign featuring a North Korean actress alongside Lee Hyori, symbolizing a bittersweet connection that persists through the tides of history.
