A drifting man in 1990s Korea
The story begins in 1988, in Seoul, South Korea. Oh Dae-su is an ordinary, unremarkable man — an office worker, married, and the father of a young daughter. On the night of his daughter's birthday, he turns up at a police station completely drunk, causing a scene and being held by officers. His friend Joo-hwan comes to collect him and gets him out, but in the brief moment when Joo-hwan stops at a phone booth to make a call, Oh Dae-su vanishes without a trace. From that instant on, his family hears nothing more from him. Shortly afterwards, his wife is announced to have been murdered, and Oh Dae-su is named the prime suspect. His daughter, left an orphan without a father, is given up for adoption to a family in Sweden.
Oh Dae-su has not fled, nor has he committed any crime. He has been kidnapped.
The imprisonment: fifteen years within four walls
Oh Dae-su wakes up in a room designed to resemble a cheap hotel room, with no windows and no means of contact with the outside world. He does not know his captors, does not understand the reason for his confinement, and no one explains anything to him. For the next fifteen years he remains locked in that space, completely cut off from the world. His only connection to the outside is a television set, through which he learns he has been charged with his wife's murder and that his daughter has been adopted. Guilt, rage, and helplessness consume him for years.
The imprisonment, however, transforms Oh Dae-su. What begins as a state of mental breakdown and despair gradually hardens into a cold and disciplined obsession. He exercises relentlessly, teaches himself to fight by striking the walls, and fills notebooks with lists of people he might have wronged over the course of his life, combing through his memories for the identity of whoever is holding him prisoner. He also attempts suicide on several occasions, without success. Over time, the desire for revenge becomes the only engine keeping him alive.
In 2003, fifteen years after his disappearance, Oh Dae-su is released as abruptly as he was captured. He appears on a rooftop, dressed in fresh clothes, with a suitcase containing money and a mobile phone. He does not know why he was let go, just as he never knew why he was locked up.
The antagonist and the true framing of the conflict
Shortly after his release, Oh Dae-su meets Mi-do, a young chef who works at a sushi restaurant. Between them an immediate and intense attraction develops, quickly evolving into a romantic and sexual relationship. Mi-do, moved by Oh Dae-su's situation, decides to help him in his search for answers.
Oh Dae-su's investigation eventually leads him to his captor: Lee Woo-jin, a young, extraordinarily wealthy, and elegant man who turns out to be a former schoolmate of Oh Dae-su's. Lee Woo-jin is not driven by an irrational impulse or a simple desire for revenge. His motivation is the product of a specific trauma, calculated with precision over decades. At school, Oh Dae-su discovered that Lee Woo-jin was engaged in an incestuous relationship with his sister Lee Soo-ah, and although he did not spread the secret intentionally, the rumour took hold. Lee Soo-ah, unable to bear the public shame, ended up taking her own life. Lee Woo-jin holds Oh Dae-su responsible for his sister's death — a sister he loved in an obsessive way — and has dedicated his entire life to constructing an elaborate and devastating act of revenge.
What Oh Dae-su does not yet know at this point, and what the viewer likewise does not yet fully understand, is that the true scope of Lee Woo-jin's plan extends far beyond mere imprisonment. The antagonist has not simply sought to punish Oh Dae-su by locking him away: he has engineered a psychological trap whose centrepiece is the very act of releasing his victim. Lee Woo-jin has manipulated every aspect of Oh Dae-su's life from the shadows, including the encounter with Mi-do, with a precise and devastating purpose that forms the core of the entire story.
The central conflict of Oldboy is not, therefore, the search for a kidnapper, but a game in which Oh Dae-su believes he is playing to uncover the truth — not knowing that the rules, the board, and the final outcome were written in advance by his adversary.