The city is infested with mysterious parasites that bore into human hosts, heightening their physical power while driving them into uncontrollable sexual frenzy. Suzune Arizono, a beautiful veterinarian specializing in parasites, fights daily to end this scourge. She soon discovers that a sinister organization, the Kito Zaibatsu, is behind the outbreak and that her long-missing father, a scientist, is somehow connected to the group.

After a violent confrontation at a research institute, Suzune is knocked unconscious. She awakens in a strange, factory-like enclosed space, having been kidnapped and imprisoned. There, she finds a fellow captive named Takaya, whose own father is collaborating with Suzune’s father. The pair learns a horrifying truth: Suzune carries a queen parasite inside her, placed there by her father years ago. The two fathers hope to force Suzune and Takaya to mate, as Takaya is the only person who has been able to host a compatible counterpart parasite without going insane or dying. Their goal is to create a new, evolved species.

Refusing to become pawns in this scheme, Suzune and Takaya attempt to escape the labyrinthine facility. They must rescue their other captive friends while fighting off violently lustful infected victims, struggling through dark corridors, and evading a mysterious girl in a maid costume who seems to be working for their captors. As they search for an exit, Suzune is forced to confront the truth about her father, who has become a madman willing to sacrifice humanity for his vision of evolution. Upon their final meeting, she realizes he is no longer the person she once knew. The film culminates in a final stand against her father’s ambitions, though the resolution remains ambiguous and incomplete, leaving the fate of the parasite queen and her companions unresolved as they fight for survival within the facility.