Nancy, Bess, and George are having a blast at the River Heights Carnival, sampling yummy snacks and trying to win prizes. The girls can't wait for their favorite local singing star, Isabelle Santoro, to perform. But Isabelle may cancel if someone's ruining all the fun with really annoying pranks. Snooty Brenda Carlton, Orson Wong, and Chloe "Cruncher" Mondesky, all make good suspects. Nancy's clue book is filling up, and she's got to solve this puzzle fast. The fun, and the show, can go on...