- Directors: Karyn Kusama
- Producers: Daniel Dubiecki, Mason Novick, Jason Reitman
- Writers: Diablo Cody
- Genres: Comedy, Horror, Sci-Fi, Thriller
- Actors: Megan Fox, Amanda Seyfried, Adam Brody, Johnny Simmons
Insecure bookworm Anita “Needy” Lesnicki (Amanda Seyfried) and arrogant, popular flag girl Jennifer Check (Megan Fox) have been best friends “since the sandbox” and wear matching heart-shaped lockets engraved with the initials BFF to signify this bond, although they share little in common. One night, Jennifer insists Needy come to a local dive bar to attend a concert by indie rock band Low Shoulder, where Jennifer soon develops a crush on their lead singer, Nikolai Wolf (Adam Brody). While flirting with Jennifer, Nikolai concludes that she is a virgin. As the band begins to perform one of their songs, a suspicious fire engulfs the bar. Needy saves a somewhat intoxicated and shocked Jennifer, who, against Needy’s wishes, ends up leaving with the band; they take her into the woods, where she learns that the band is worshiping Satan and that Nikolai intends to use her as a virgin sacrifice in order to become famous. However, as Jennifer is in fact not a virgin when Nikolai murders her, a demonic spirit takes over her body with all her memories still intact after Nikolai and the band leave. Later that evening, Jennifer appears at Needy’s house, covered in blood. She resists attacking a terrified Needy and instead roams into the kitchen, where she tries to eat food from the refrigerator; unable to digest the matter, she vomits a trail of black ferromagnetic fluid. She then leaves the house in a hurry as Needy calls after her. Needy, left frightened and alone, believes something horrible has happened to Jennifer.
Needy is committed to an asylum for the criminally insane. Since she was bitten by Jennifer during their fight, she obtained some of Jennifer’s supernatural abilities and murderous instincts. With these powers, she eventually escapes the facility and comes across the knife that Low Shoulder’s Nikolai used to kill Jennifer. Set upon revenge, she hitchhikes a ride, saying to the driver (cameoed by Lance Henriksen) that she is following a band and that “tonight is gonna be their last show”. She soon finds and butchers them all.