Jennifer Check (Megan Fox) is a sexy, popular captain of the flag team that everyone wants to be friends with and, in the boys' case, date. Jennifer's friend since childhood, Anita "Needy" Lesnicky (Amanda Seyfried), is a substantially less popular nerdy plain jane. Jennifer ends up as the sacrifice in a Satanic ritual, held by a rock band, hoping that the sacrifice will increase their chances of getting a record deal. The ritual goes horribly wrong and Jennifer becomes possessed by a demon and begins to feed off of the boys in her high school—first seducing them to get close, and then consuming them in a manner similar to that of a Succubus. It becomes Needy's goal to stop Jennifer from killing more of her classmates.