Bess's mom is on the board of Pet Crusaders, a local rescue organization, and hosts the charity's annual fundraising gala. Nancy, Bess, and George have attended the event ever since they were kids, and they're excited for this year's party, the theme of which is "A Night on a Riverboat."

The gala will feature blackjack, roulette, and a high-stakes poker tournament, and all proceeds will go to help stray animals. But when the charity money goes missing mid-event, Nancy has to track down the thief--before the ship docks.

With three hours and over two hundred guests, Nancy faces one of her greatest mystery-solving challenges yet