Kim Levitt is an aspiring journalist working for the newspaper, L.A. Eye, as a classified ads editor. Her sexist boss, Eli, seems to give all of the men in her office the breaks, including her boyfriend Hank. When a woman is discovered dead on the sidewalk, half-burned to ashes in an apparent case of spontaneous human combustion, Kim decides to pursue the story on her own without Eli's approval. Her first stop is Munn Fresh Meat, a butcher shop run by Jo near the site of the suicide's landing. Kim asks him about the jumper. He tells her that the suicide probably got to the roof of the building she jumped from through the apartments there.
Around the corner, she enters a used book store. Kim asks for a book on spontaneous combustion, which the proprietor, Fima, finds for her. At checkout, she insists that Kim take another book from her, Initiation of the Virgin Goddess. Kim initially refuses, but Fima insists and declares it her invitation to a picnic she's having with friends the next day. Fima shows Kim the way to the roof of the building. Kim inspects the spot where the jumper leapt from and tests it herself by standing on the ledge. Behind her, Ricky (a slave) arrives. He sticks his head in a ventilation pipe as Kim approaches him. From inside, Ricky pulls out a large, slimy insect larva. He shows it to Kim, who screams and runs off.
Back in her own apartment, Kim discovers her sink is full of cockroaches; she frantically sprays insecticide on them. She settles down on the kitchen table to eat dinner and flips open the book Fima loaned her. The page she randomly arrives at is titled "The Spiral: Symbol of Women's Power". Kim glances at her plate of noodles and notices that they are arranged in a vague spiral. She spies another roach crawling out of a loaf of bread. Using the book, she bats at it. In the process, her spaghetti dish crashes to the floor. Leaving it on the floor, she leaves to spend Christmas Eve with Hank's family.
At Hank's parents' house, his mother Ann serves drinks and snacks, his father Gus guzzles beer and his little brother Lonnie shakes the presents under the Christmas tree. When Kim tries to explain to Lonnie that even though she's Jewish, that Hanukkah and Christmas are just two different holidays that deal with the same thing in their different ways, Gus gets upset. When Kim talks about her job at the Eye, Gus says that he believes a woman's place is in the home since Eve was made from Adam's rib. Hank testily replies that that story is just an allegory, but Gus disagrees, claiming it is "goddamned real".
When Kim returns to her apartment, she scrapes the dead roach from Fima's book and flips it open. The page she randomly lands on is titled "The Fire of Lilith" and it depicts a woman whose lower half is engulfed in flames. Kim glances down at the plate of spaghetti on the floor. The spaghetti is now arranged in a flame-like pattern. Across from the spaghetti, she thinks she see a giant roach under the couch. She throws the book at it and it scurries off. She looks, but is unable to find it. While looking, she notices the spaghetti on the floor pulsating. She gets violently ill and passes out on the floor. Knocking on the door from her coworker Janice wakes her up the next day. Kim decides not to go to work and instead drives to Fima's picnic. There, the motherly Fima introduces her to Katherine Harrison (Jeanne Bates), a self-described old crone, and the young Jane Yanana. They tell her about Lilith, Adam's first wife and the "spirit of all that crawls". Kim begins to feel the effects of the wine they are drinking and lays down. Just as she begins to see something in the tree branches above her, Hank arrives and drives her to work.
At the Eye, Eli, instead of being angry about Kim not showing up for work all morning, lets her officially have the spontaneous combustion story. Kim wonders how Hank knew where to find her. He says that Janice told him. When Kim asks Janice how she knew, Janice claims that Kim herself had told her. Hank and Kim return to the roof to investigate the story further. There, they find a spiral drawn on the ground as well as Ricky's lean-to. Hank leaves and Kim decides to visit Fima's apartment. Fima serves her a cup of tea, which makes Kim nauseous at first and sleepy later. Fima tells Kim of her daughter Lilith, whom Kim reminds her of. Fima offers her another date and demands that Kim eat it. She does, even though it looks like a roach in her hand. Soon after, Kim passes out.
She awakens surrounded by Jane, Fima, Katherine, and Li; they strip her of her clothes and paint a dark line from her forehead to her chin and a spiral around her navel. Ricky brings in the same larva from the ventilation pipe, and he places it on her stomach. As Katherine chants a spell and Ricky and Fima slice open a live rat over her, the larva crawls into Kim's body. Under her skin, the larva crawls up Kim's body. It emerges from her mouth as a full-grown, giant, multi-segmented roach; Kim vomits the creature out. Ricky slices the creature in half and drips its innards onto Kim's face in a near-sexual manner. Kim wakes up later fully dressed, still in Fima's apartment. The four women encourage her to stay, but she escapes and runs home. There she finds Hank waiting for her. The stressed Kim starts a fight with him, but he calms her down and they begin to make love. While doing so, Ricky casually enters the apartment, sits on their bed and begins watching TV. When he flips to a channel showing a clip from Silent Night, Deadly Night 3: Better Watch Out!, he laughs. The noise alerts Hank, who demands that Ricky leave. They scuffle and Hank is stabbed to death by Ricky. Kim manages to answer her ringing phone during the fight and screams for Janice to help her. Ricky captures Kim and binds her. Janice arrives, but doesn't help Kim. Instead, she admonishes Ricky for the mess and tells him to take Kim straight to Fima while she cleans up.
Ricky locks Kim in the meat locker at Munn Fresh Meat where she passes out again. When she awakens, she is surrounded by the entire cult. Fima places her in a chair and tells her "it's not easy to give birth to yourself." Ricky, wearing a phallic mask, rapes Kim. Kim reawakens alone in the meat locker; at first her fingers bind themselves together in a knot. Then she experiences incredible pain as her legs bind together into an insect-like tail. Kim passes out one more time. She awakens in the meat locker as Jo opens the door. She frees her legs from a brittle cocoon-like substance and covers her as best as she can. Jo tells her that she has been initiated and that she should go.
Kim returns to Fima's bookstore where Fima admits that the woman who jumped was her daughter Lilith and that she wants Kim to take her place. She explains that the experience Kim just had has freed her from men and the fear that they bring. Kim believes she was simply hallucinating, but Fima insists that she created everything that she saw using the magic within her. Fima then reveals that she must kill a man in order to complete her initiation or else she will be consumed by fire just as Lilith was, and Kim refuses. Kim brings a policeman, Detective Burt, to her apartment. There, everything is spotless and there's no trace of Hank's body. At her office's Christmas party, Eli claims that Hank is away on assignment. Janice there welcomes her to the family. Furious and confused, Kim storms out of the office and walks down the sidewalk. She notices Ricky following her and ducks into a motel room. Her feet begin to get painfully hot. She jumps into the shower, but they still burst into tiny flames. Ricky enters the room and, in pain, Kim agrees to kidnap Lonnie to complete the initiation.
Kim lures Lonnie out of Hank's parents' house and into a waiting van. When Ann goes to investigate, Ricky tapes her mouth shut and strangles and electrocutes Gus with a string of Christmas lights. As the house begins to burn, Ricky jumps into the van and they drive back to Fima's rooftop. With Lonnie tied up on the roof, Fima hands Kim a knife and tells her to kill him. Kim refuses and instead stabs Fima. In anger, Fima pulls the knife from her belly and stabs Ricky. Giant larva feed on the wounded man as Kim's legs begin to get hot. Kim's hands knot themselves into together once again, then they start on fire. She stabs her modified, flaming hands into Fima's knife wound. This transfers the curse of Lilith to her, who dives off the roof just as her daughter had. Kim hugs Lonnie and tells him that it's all over.