The film opens with a gripping scene where Oh Dae-su (portrayed by Min-sik Choi) is holding another man suspended by a necktie over the edge of a building, insisting that the man must listen to his tale. The story then takes a compelling turn, transporting us back to 1988, where Dae-su lives a seemingly typical life as a businessman, accompanied by his wife, Kim Ja-Hyun (played by an unidentified actress), and his beloved daughter, Yeun-Hee.

On his daughter’s fourth birthday, Dae-su finds himself in a drunken stupor, leading to an incorrigible disturbance at the police station. Amidst this chaos, he showcases angel wings he purchased for his daughter, only to be bailed out by his loyal friend, Joo-Hwan. Meanwhile, as Joo-Hwan converses with Dae-su’s family, danger looms as Dae-su is unexpectedly kidnapped by masked figures.

Fast forward two months, Dae-su is trapped in a dingy makeshift prison, deprived of both freedom and knowledge about his captors. He receives mysterious meals and is frequently gassed into unconsciousness. The stark reality of his situation hits him when he learns via the television news that his wife has been brutally murdered, his daughter is gone, and he himself is the prime suspect. As despair wraps around him like a suffocating shroud, Dae-su descends into a state of madness, punctuated by violent hallucinations.

Determined to maintain his sanity, he begins documenting his thoughts in a series of notebooks, mapping out all the potential foes from his past. As the years roll by, he tattoos the years of his captivity on his arm and trains tirelessly through shadowboxing, while quietly engineering an escape route. After a decade of agonizing isolation, he discovers a chopstick in a food delivery that becomes his tool for digging out.

In a twist of fate, Dae-su is suddenly set free one day, finding himself on the rooftop of a newly constructed building. Not accustomed to the freedom, he encounters a suicidal man who shares a poignant sentiment: > “Even though I’m no better than a beast, don’t I have the right to live?” Dae-su, deeply affected, offers the man a glimmer of hope, asking him to hold off on his demise so he can unravel his own dark tale.

As he navigates through the city streets, burdened with his newfound liberty and the weight of false accusations against him, Dae-su encounters a gang, where his years of training come to fruition, allowing him to fend them off effortlessly. Later, he meets Mi-do, a sushi bar employee who bears a striking resemblance to someone from his memories. A mysterious call soon introduces Dae-su to his captor, who brazenly discloses that the imprisonment was part of a chilling experiment, leading Dae-su down a dark rabbit hole of secrets to uncover.

In his pursuit of the truth, Dae-su learns that the clues left for him intertwine with the tragic fate of his past and others, including his connection to Mi-do. The narrative spirals into a frenetic race against time, involving old grudges and the re-emergence of figures from his past, culminating in shocking revelations about Dae-su’s past actions toward Woo-jin (played by Yu Ji-tae) and his sister.

This harrowing journey of vengeance and revelations extends beyond comprehension, as Dae-su confronts the haunting consequences of memory, regret, and desire. Dae-su’s unique struggle peaks as he grapples with the notion of familial ties in the most horrific sense, all while trying to protect Mi-do. Dae-su’s descent into madness, interspersed with visceral moments, reflects his battle within, only to be met with a heartbreaking climax that beckons existential questions about love and suffering.

In the end, Dae-su seeks help to erase the memories that torment him, echoing the haunting lines first heard from the despondent man he saved. Torn between love and monstrosity, he is left to grapple with the shadows of his choices as he faces an uncertain future with Mi-do, culminating in a complex embrace charged with agony and hope.