Anita "Needy" Lesnicki, once an insecure and studious teenager living near Devil's Kettle, Minnesota, is now a violent mental inmate who narrates the story as a flashback while in solitary confinement. Since childhood, she had been friends with Jennifer Check, a popular cheerleader, despite having little in common. One night, Jennifer takes Needy to a local dive bar to attend a concert by indie rock band Low Shoulder. A suspicious fire engulfs the bar, killing several people. In shock, Jennifer agrees to leave with the band, despite Needy's protests. Later that evening, Jennifer, covered in blood, appears in Needy's kitchen and attempts to eat food from the refrigerator. She immediately vomits a trail of black, spiny fluid and leaves in a hurry.
The next morning at school, Jennifer appears fine and dismisses Needy's concerns. While the town is devastated by the deaths caused by the fire, Jennifer seduces the school's football captain in the woods and disembowels him. Meanwhile, the members of Low Shoulder gain popularity due to their falsely-rumored heroism during the fire and offer to make a charity appearance at the school's spring formal.
A month later, Jennifer appears sick and listless. She accepts a date with school alternative/emo Colin, whom she brutally kills. While Needy and her boyfriend Chip have sex, Needy senses something dreadful has happened.
