In Cleveland, Ohio, high school senior Karen “Wren” DeSantis' opening narration describes Halloween in Cleveland as a time for its citizens to dress up and be less ashamed of themselves, citing the nickname "the mistake by the lake." Wren's widowed mother, Joy, is dating a 26-year-old named Keevin. Wren has her heart set on college life at New York University. Her friend April has her eyes set on social status, and Wren's nerdy friend Roosevelt has his heart set on Wren. The two girls are surprised when they find they are invited to a Halloween party by local heartthrob Aaron Riley. Unfortunately, on the day Wren is supposed to go to the party, she is commanded by her mother to take her 8-year-old brother Albert trick-or-treating so she can go to a party with Keevin. The party that Keevin invites Joy to turns out to be run by Keevin's friend Nate Brueder. At a haunted house later that night, Wren and April run into Roosevelt and his best friend Peng. Albert meets a convenience store employee named Fuzzy who seeks revenge against Jörgen, a mixed-martial arts fighter, who won the heart of his ex-girlfriend Lara. Roosevelt's parents are revealed to be semi-eccentric pacifistic lesbians.