When the rubber duckies for River Heights's duck derby go missing, Nancy and her friends are ready to quack the case in the sixteenth book in the interactive Nancy Drew Clue Book mystery series. River Heights is hosting a duck derby to raise funds to install new benches by the pond in the park. Nancy, Bess, and George want to help, so they ask Mayor Strong if they can number the rubber duckies that will be used in the race. It's...