Shirō is a student who is about to marry his girlfriend, Yukiko, the daughter of his professor, Professor Yajima. After the engagement is announced, Shirō’s colleague Tamura drives him home and, at Shirō’s request, takes a side street. On that street, Kyōichi, a feared yakuza gang leader, is fatally struck by the car. Kyōichi's mother, Kyōichi's Mother, who witnesses the crash, vows to hunt them down and exact revenge.
Tamura feels no guilt for the hit-and-run, while Shirō is wracked with remorse and contemplates going to the police. After telling Yukiko what happened, Shirō insists they take a taxi to the station, despite Yukiko’s pleas to walk. The taxi crash that follows kills Yukiko, and her funeral soon after deepens Shirō’s sense of loss and responsibility. At the funeral, Shirō encounters Yoko, a strip-bar worker and Kyōichi’s grieving girlfriend. Yoko learns of Shirō’s role in the accident after spending the night with him, and, together with Kyōichi’s mother, begins to plot revenge.
As Shirō mourns, he learns that his mother, Ito, who lives in a retirement community run by his father, Gōzō, is dying. At the community, Shirō meets a painter named Ensai, a former reporter named Akagawa, a corrupt detective named Hariya, the community doctor Dr. Kusama, and Sachiko, a nurse who bears a striking resemblance to Yukiko and who is Ensai’s daughter. Ito’s death sets off a fierce confrontation: Ensai, once Ito’s lover, chastises Gōzō for his years-long affair with a mistress. Tamura returns and reveals that every resident at the home bears some complicity in past murders—Yajima’s apparent war-time killing, Hariya and Akagawa’s frames that led to suicides, and Kusama’s misdiagnosis.
Yoko tracks Shirō down and confronts him on a rope bridge, revealing her identity and attempting to shoot him. She trips and falls to her death, and Tamura reappears, only to fall into the gorge after a struggle. Shirō then attends the community’s tenth anniversary party, where Gōzō has allowed cheap, rancid fish to be served. As the party devolves into intoxication and chaos, Mr. and Mrs. Yajima kill themselves by leaping in front of a train, and Gōzō’s mistress dies during a heated confrontation. The tainted fish claim the lives of many residents, and Kyōichi’s mother poisons the remaining wine. Tamura, nearing death, staggers into the party and shoots Sachiko; in a fit of rage, Shirō strangles Tamura, while Kyōichi’s Mother exacts her own fatal retribution.
In Limbo, Shirō meets Yukiko again, who reveals she was pregnant when she died and that she sent their baby girl, named Harumi, floating away on the Sanzu River. She pleads with Shirō to save his child. Shirō descends into Hell, where Lord Enma judges him for his sins. There, he witnesses the torments of those from his life—boiling, burning, flaying, and endless cycles of punishment—before Tamura taunts him with the illusion that there is no escape. Shirō searches for his daughter and encounters Sachiko, only to be confronted by Ito, who reveals that Sachiko is her daughter and Shirō is Ensai’s son. In a harrowing moment, Shirō sees his baby daughter spinning on a massive wheel as damned souls swirl around him; Lord Enma grants him a single chance to save her, but Shirō, bolstered by calls from Yukiko, Sachiko, and his mother, cannot reach Harumi in time.
Back in the living world, the party has ended in tragedy: Ensai has hanged himself after finishing his Hell portrait and setting it ablaze. In a final, poignant image, Sachiko and Yukiko appear, smiling and calling to Shirō as sister and lover, while lotus petals drift down, implying that Shirō’s effort to save his daughter may have freed their souls to ascend to Heaven.
