<P> After a biology class, Dr. Gregory is killed by an unseen monster, which only shows a pair of large eyes and an insectile limb . The next day, Buffy is alarmed by news of Dr. Gregory's disappearance, but the boys in her class are more interested in the beautiful substitute teacher, Natalie French (Musetta Vander), who seems to have a fixation on insects, especially the praying mantis . Miss French suggests making model egg sacs for the upcoming science fair and asks the class for help . She selects Blayne as her lab partner for that day, to be followed by Xander the next day . </P> <P> Cordelia finds the headless body of Dr. Gregory inside a cafeteria refrigerator . That night Buffy goes into the park and confronts a vampire who has a large claw in place of his right hand . They fight but are interrupted by the police and the vampire escapes . It encounters Miss French while she is walking home with groceries and flees in terror, indicating that Miss French is not human . </P> <P> The next day Buffy is late for her Biology class and is horrified to watch as Miss French seems to sense somebody at the door and then turns her head 180 degrees to see who it is . After the class, Miss French claims to have left supplies at home so she asks Xander to come over to her house that evening and work on the egg - sac project there instead . </P> <P> Back in the library, Buffy realizes that Blayne never returned home from helping Miss French . Giles recalls a creature known as the "She - Mantis", or the "Virgin Thief", which preys on virgin males to fertilize its young . That night, Xander arrives at Miss French's house to find her wearing a tight dress and acting in a sexually suggestive manner . She offers him a drink, which he takes and then collapses . She turns into her mantis form and takes his body to a cage in the basement, where he wakes up next to Blayne . </P>

Buffy the vampire slayer season 1 episode 4