Seok-tae, a drug addict and gangster, is found dead under suspicious circumstances. His brother Min-tae, who has distanced himself from the criminal world, begins a dogged search for the killer. Meanwhile, Seok-tae's wife Moon-young and their child vanish, triggering a police investigation as tensions rise within the local underworld. The case quickly spirals into a web of power and obsession, where every lead seems to pull investigators deeper into the shadows of the city’s elite.
Prior to his death, [Seok-tae] had been involved in drug distribution connected to the son of a powerful CEO, who falls into a coma after consuming narcotics allegedly supplied by him. Chang-mo, Seok-tae's boss and Min-tae's former superior, warns Min-tae not to interfere, hinting that influential figures move the pieces from behind the scenes. The atmosphere is tense, and fear quietly threads through both the streets and the offices that loom over them, suggesting that the killing may be only the visible tip of a much larger conspiracy.
Suspicion gradually centers on Moon-young. It is revealed that she had endured years of domestic abuse at the hands of Seok-tae, a history that fuels a bitter ambiguity about her role in the tragedy. Her connection to renowned novelist Kang Ho-ryeong further complicates the case. Kang’s name carries weight, and his literary exploration of crime foreshadows events strikingly similar to Seok-tae's death in his novel Nocturnal, which was written before the crime occurred. As investigators learn that the novel was inspired by Moon-young's experiences, both the police and Min-tae grow convinced that she may have played a role in orchestrating the murder, even as they struggle to separate truth from the trauma that surrounds them.
Determined to find her, Min-tae recruits Byung-gyu, one of Chang-mo's subordinates, while Kang searches for Moon-young in an effort to protect her. The pursuit unfolds through a maze of interrogations, stakeouts, and uneasy alliances, as the city hums with the tremors of a crime that seems increasingly personal despite its corporate shadows. After a series of confrontations, Moon-young secretly reveals her location to Kang, and Min-tae follows him to a bus terminal where Min-tae, Kang, Moon-young, and the police converge in a tense, final moment of truth.
Before the truth can fully emerge, Byung-gyu suddenly kills Moon-young and flees. Enraged, Min-tae pursues him and discovers that the killing was ordered by Chang-mo. The revelation exposes Chang-mo as the true mastermind behind Seok-tae's murder, a man who orchestrates violence to placate powerful interests and to maintain a grip on both the underworld and the boardrooms that fuel it. On the night of the incident, both Seok-tae and the CEO's son had consumed large quantities of drugs; when the CEO's son fell into a coma, Chang-mo executed Seok-tae to appease the CEO, revealing a chilling calculus at the heart of the case.
It is also revealed that Moon-young had been a direct witness to Seok-tae's murder and had long wished for his death after years of abuse. Chang-mo had spared her out of sympathy and on the condition that she disappear permanently. Following Seok-tae's funeral, Min-tae confronts Chang-mo, kills his men, and forces a confession confirming his responsibility and the gang's subservience to corporate influence. Min-tae ultimately kills Chang-mo and walks away, leaving behind a cloud of questions about loyalty, power, and the price of justice in a city where criminals and executives share a fragile, dangerous kinship.
