The She Mantis (Musetta Vander) infiltrates Sunnydale High by killing
Buffy's favourite teacher, Dr Gregory, whose decapitated body is found
in the school canteen refrigerator. The shape-shifting, insect-like
She Mantis then gets his job by assuming human form (as a beautiful
young woman) and the identity of a substitute teacher, Natalie French.
Quickly winning over the male students including Xander, she soon
has candidates lining up to become her mate, who are unaware that
they'll die in the process. However Buffy, who has seen her head
rotate round in a "full-on Exorcist twist", is highly suspicious
and rushes to the rescue...