Inside a shipping container, customs agents discover a huge amount of human hair used as materials for hair extensions, along with the body of a young girl with a shaved head. The corpse is transported to the morgue, where it is discovered that the girl's internal organs have been harvested by illegal organ traffickers. The morgue's night watchman, a tricophile named Yamazaki, is infatuated by the girl's hair and steals the body. He finds that the body has begun to grow hair everywhere: its head, vacant eye sockets, tongue, and open wounds. A delighted Yamazaki harvests the hair to make hair extensions to sell. However, the hair controls and kills its wearers, causing them to experience the dying memories of the dead girl, including the last thing she saw on the operating table: the smiling mouth of the man who killed her. Yuko is a young apprentice hair stylist at a local salon. Her irresponsible older sister, Kiyomi, dumps her eight-year-old daughter, Mami, on Yuko and her roommate Yuki. By happenstance Yamazaki encounters Yuko and Mami and find their hair beautiful. He comes to Yuko's salon the next day with his hair extensions, which her co-workers are impressed with. That night, Kondo, one of Yuko's co-workers, is killed when the hair begins sprouting from her eyes, head, and mouth. It is revealed through a flashback that the dead girl's head was shaved by her kidnappers before her murder. Meanwhile, Yuko and Yuki refuse to return Mami to Kiyomi due to her abuse of the child. Kiyomi returns while they are away and drags Mami back to her boyfriend's home, taking some of the hair extensions with her. After Mami is locked in a closet, the extensions kill Kiyomi and her boyfriend. Mami escapes the hair by jumping out of the window, injuring herself. Yuko later uses Mami as her model in a hairdressing workshop and attaches one of Yamazaki's hair extensions to her hair. The workshop is interrupted by detectives investigating Kondo's death. Yuko realizes that the hair extensions are the linking factor in the deaths and races home to save Mami. Yuki is strangled to death by the hair and Mami faints. Yuko arrives into the hair-filled apartment but is choked unconscious by the hair. Yamazaki arrives and commands the hair to spare Mami and Yuko. He takes them back to his hair-covered home. There, he discovers the detectives caught in the hair, who searched his house because of the deaths. He kills them as Yuko wakes up. Yamazaki explains that the girl's hair keeps growing to carry on her grudge against society. He wishes for Mami and Yuko to stay with him and the corpse forever. Yuko rejects him; Yamazaki, enraged, reveals that he allowed the hair to possess him, his tongue hairy and his blood and limbs replaced by hair. In anger, he cuts some of Mami's hair, which begins to bleed. The blood and Yamazaki's smiling cause the corpse to associate him with the man who killed her and she suddenly sits up and slices him to pieces with strands of hair while Yuko and Mami escape. Her grudge satisfied, the hair disappears and the girl's body returns to normal, finally at peace. Yuko asks Mami to live with her permanently, which Mami happily accepts.
