Nancy, Bess, and George are having a blast at the River Heights Carnival, sampling yummy snacks and trying to win prizes. Most of all, the girls can't wait for their favorite local singing star, Isabelle Santoro, to perform. But Isabelle may cancel if she finds out that someone's ruining all the fun with really annoying pranks.

Snooty Brenda Carlton, annoying Orson Wong, and Chloe "Cruncher" Mondesky, the pie-contest queen, all make good suspects. Nancy's clue book is filling up, and she's got to solve this puzzle fast—so the fun, and the show, can go on!