Jay (Jason London) and Hannah (Alyssa Milano) are madly in love, so much so that he respects her chaste request to wait until marriage to make love. But one night, a strange object falls into Hannah's room, and emits a mysterious green glow, enveloping her and embedding itself into her body. Hannah is now possessed. She craves sex, and to feed the alien presence within her, she must prey upon willing males who morph into her body while making love. Hannah first approaches Jay, of course, who cannot believe this was the same girl who steadfastly denied him just the night before. And indeed, she isn't the same girl. When Hannah seduces the star Quarterback, Jay follows them in disbelief. He finds Hannah alone and notices the hole in the ceiling where the alien object entered her room. Realizing that Jay is in danger while in her presence, Hannah forces him to leave, but Jay steals back to her room later and discovers the remains of the object and the Quarterback's jacket. Investigating the disappearance of the Quarterback, the police trace Jay to the scene, and he becomes the prime suspect. Jay turns the object over to his professor, who determines its origin, and researches similar occurrences. As more men vanish, the police pursue Hannah, who is then "caught in the act" devouring a convenience store clerk. A cop shoots Hannah, and to his utter horror, the undevoured top half of the clerk drops to the ground to die. He then watches as the violet light emanates from the bullet hole in her stomach. Hannah is rushed to the hospital and doctors watch in awe as the wound heals itself. The professor is able to substantiate Jay's outrageous claims, and when the police release him, he rushes to the hospital to be with Hannah. Desperate for fresh victims, Hannah attacks her doctor, who refuses to give in to her obsession. Certain that his love is more powerful than the force within her, Jay risks his life to try to cure Hannah. Fearing for Jay's safety, Hannah tries to resist him and the craving within her, and ultimately, the purity and power of their love forces the alien presence from her system.