That night at the Bronze, Buffy sees Angel; who tells her that there is a new vamp around. Buffy notices a scar on his arm and asks if the new vamp did it. He tells her yes and explains that this vamp has a pitchfork thing for a hand. He says she looks cold and gives her his leather jacket.
The next day, Dr. Gregory is absent and in his place there is a 'hot' new teacher named Natalie French. She discusses the praying mantis and asks the young men in the class to help her construct paper mache egg sacks. That day, a jock named Blayne is working with her, but Xander has the next day.
At lunch, when Cordelia is getting her special lunch from the refrigerater, when Dr. Gregory's headless body tumbles out. Buffy hears her screaming and rushes in time to identify the body by the name tag on the lab coat.
Buffy suspects that the vampire with a fork might have killed Dr. Gregory, so she goes looking for him. She finds him and they fight, but he gets away and flees over a wall. Buffy sees him attack Miss. French, but she turns and gives him a look and he runs away scared.
Principle Flutie insists that all students who saw the dead body attend counseling. After her counseling session, Buffy goes to science class and peers inside the door and sees Miss. French do a 180 with her head. Freaked out, Buffy waits for Willow and then they go to Giles to figure out what's wrong. They look it up and find that the most likely explanation is that Miss. French is a preying mantis. Giles makes a few calls and they figures out how to kill it. Meanwhile, Xander is being given a martini at Miss. French's house. He drinks it and she asks him if he's ever been with anyone. Being drugged, his thoughts are scattered, but one thing is clear. He blurts out that he loves Buffy. Then he passes out.
When he awakens, he is in the basement in a cage with Blayne. Blayne tells him that the creature will do some weird mating thing with him. Terrified, Xander tries to find a way out. Around the same time, Buffy recalls that Xander is going to see Miss. French, and they try to find him. But, when they go to the registered address for Natalie French, there is an eighty-something woman there. Buffy locates the fork guy and makes him lead them to Miss. French. She bursts into the basement to save Xander and plays batsonar; which disables the mantis's system and Buffy 'slices and dices' it.
The group gets a new science teacher, but Buffy still misses Dr. Gregory. After class, she takes a pair of his broken glasses and places them in his lab coat pocket. She places the jacket in Dr. Gregory's closet and then the camera reveals mantis eggs hatching in the corner.