A successful but creatively bankrupt novelist prowls the late-night streets of 1970s Shinjuku, trapped in a downward spiral of empty celebrity and his own dark desires. Yosuke Mikura, once a respected literary voice, now churns out shallow work while wearing his signature dark glasses as a shield. He is engaged to the daughter of a powerful politician, a relationship that pushes him further toward a life of cynical sell-out compromises. His existence is one of comfortable desperation, haunted by sexual obsessions that increasingly detach him from reality.

One evening, he discovers a beautiful young woman passed out drunk in a dingy underpass. Acting on an impulse he cannot explain, he takes the disheveled stranger, who calls herself Barbara, back to his immaculate apartment. Far from a damsel in distress, Barbara is a wild, chaotic force. She swills his expensive whiskey, behaves obnoxiously, and yet displays an uncanny intelligence, having read all of his novels and casually quoting French poetry. She is also brutally honest, accusing him of betraying his talent. Though he initially throws her out, Yosuke finds himself obsessed, and Barbara becomes an inescapable fixture in his life.

As Yosuke’s obsession deepens, the boundaries between his perverse fantasies and reality begin to crumble. In one hallucinatory encounter, he follows a flirtatious shopgirl into a dressing room, only for Barbara to appear and tear the woman apart, revealing her to be a mannequin. At his fiancée’s house, he mistakes her long-haired dog for a woman in a flowing dress, nearly acting on his delusion before being snapped back to reality. Barbara seems to appear at these critical moments, rescuing him from his most bizarre impulses and, for a time, jolting him out of his writer’s block. She becomes his muse, but her presence introduces a sinister and occult dimension into his life.

Yosuke’s investigation into Barbara’s origins leads him away from the glamorous literary world and into the seedy underbelly of Tokyo’s gothic subculture. He eventually encounters her mother, the grotesque and powerful Mnemosyne, named after the Greek goddess of memory, who presides over a witches' coven. It is here that Yosuke realizes Barbara may not be entirely human, but an actual muse or a supernatural being. He is drawn into a dark marriage ceremony with her, a ritual that plunges him fully into a world of depravity, sex cults, and black magic. The story descends into its grim conclusion as Yosuke’s career, relationships, and sanity are completely destroyed. The film ends in a place of tragic loss and ultimate taboo, touching on themes of madness and necrophilia, as the writer is consumed by the very force that briefly reignited his creativity.