A botched government mission plants the seeds for a twenty-eight-year revenge scheme in the 2011 South Korean television drama City Hunter. The story begins in 1983 with the Rangoon bombing, a real-life political attack. In the series, this event leads five high-ranking South Korean officials to secretly order a retaliatory covert operation into North Korea codenamed Cleansweep. When the mission is abruptly aborted to avoid an international scandal, the officials order the naval extraction team to kill the twenty-one commandos to erase all evidence of the plot. Only two presidential bodyguards survive the massacre: Lee Jin-pyo, who is gravely injured, and Park Moo-yul, who sacrifices himself to save his friend. Vowing revenge on the five traitors, Jin-pyo kidnaps Moo-yul's infant son, renames him Lee Yoon-sung, and flees to the Golden Triangle to raise the boy as a weapon.

Years later, Yoon-sung has earned a doctorate from MIT and returns to South Korea under a false identity. Jin-pyo orders him to infiltrate the Blue House, the presidential palace, as an IT expert. From there, he is to systematically destroy the five officials, who have since become powerful and corrupt figures controlling politics, finance, and organized crime. However, Jin-pyo and Yoon-sung clash over methods. The ruthless father figure wants to murder each target, while the younger man prefers to expose their crimes and let the law take its course. As Yoon-sung begins executing elaborate schemes to reveal each official's corruption, the public becomes aware of a mysterious vigilante bringing down powerful villains. The media dubs this phantom of justice the City Hunter.

Complicating his mission, Yoon-sung works closely with Kim Na-na, a skilled martial artist and a member of the presidential security detail assigned to the Blue House. Despite Jin-pyo's strict warning to never fall in love because it would endanger everyone around him, Yoon-sung grows close to Na-na, who eventually discovers his secret and joins his cause. The situation becomes even more complex with the introduction of Kim Young-joo, a fiercely principled prosecutor who is the son of one of the five targets. Young-joo is a legal rival to the City Hunter, trying to bring the same men to justice through the courts while simultaneously trying to uncover the vigilante's true identity.

The central conflict intensifies as the body count rises. Jin-pyo, losing patience with Yoon-sung's mercy, begins killing off the targets himself. This forces Yoon-sung to choose between his loyalty to his adoptive father and his own moral code. A major twist reveals that the current President of South Korea, Choi Eung-chan, is the fifth and most powerful member of the original Council of Five. It is also discovered that the president is Yoon-sung's biological father, born from an affair before Park Moo-yul agreed to raise the child to protect his mother. This revelation brings the revenge cycle full circle, forcing Yoon-sung to confront his two fathers: one who raised him as a tool for murder and one whose political ambition led to the original massacre. The narrative culminates in a confrontation where Yoon-sung must prevent Jin-pyo from assassinating the president, ultimately seeking a form of justice that breaks the endless chain of vengeance rather than perpetuating it.