Help investigate the case of a missing lemonade recipe with Nancy and her friends. The girls want tickets to see pop singer Katy Sloan play at the River Heights Amusement Park -- but their parents say they've already filled their summer theme park quota. So the girls decide to turn lemons into lemonade by earning their own tickets -- with a lemonade stand! Unfortunately Lily Ramos, a new girl in River Heights, has the same idea. She's the niece of the owner of the town's newest and hottest cafe, and her stand is equipped with cafe tables, gourmet treats, and a rolling library cart! Good thing Nancy has a secret weapon: Hannah's family lemonade recipe! The girls are all set to whip up the lemonade -- until the recipe is replaced by a blank sheet of paper! Nancy, Bess, and George set out to find the thief!