Nerdy, reserved bookworm Anita "Needy" Lesnicki (Amanda Seyfried) and arrogant, conceited flag girl Jennifer Check (Megan Fox) have been best friends "since the sandbox", although they share little in common. One night, Jennifer drags Needy to a local dive bar to attend a concert by indie rock band Low Shoulder, with eyes on its blithely evil lead singer, Nikolai Wolf (Adam Brody). While flirting with Wolf, Jennifer insinuates that she is a virgin. A disastrous fire destroys the bar, and Jennifer ends up leaving the bar with the band, who take her into the woods, where she learns that the band is worshiping Satan, and that Wolf intends to use her as a virgin sacrifice in order to gain fame. However, as Jennifer was not a virgin, the demon spirit takes over her body. Later that evening, Jennifer appears at Needy's house, covered in blood, looking vacant, and vomits a trail of "black ferromagnetic fluid".[2] The following morning, Jennifer appears fine, and the small town is devastated by the destruction of the local bar. A month after the incident Jennifer is beginning to look pale and tired. That day, Colin (Kyle Gallner) asks her on a date and that night she kills him brutally while Needy and her boyfriend Chip have sex. Needy senses this and leaves Chip's house in a panic. While driving she almost runs over Jennifer covered in someone else's blood. Needy rushes home and goes to bed. There she finds Jennifer who explains what happened that night after she left the bar with the band. She even goes to show Needy what happens when she is "full" and stabs herself and the cut heals almost immediately. Needy then kicks her out of the house and Jennifer jumps out of the second story window and vanishes. The next day at school the news of a death of yet another classmate stuns the school. Needy goes to the library into the occult section to do research and finds that Jennifer is weakest when she is hungry and must eat flesh in order to sustain her life and appearance. Needy surmises that Jennifer is eating the bodies of boys to survive.