In Canada, the Aldens explore Niagara Falls. They meet Will LaSalle who runs LaSalle's Curiosity Shop. The shop needs some organizing and cleaning up, and naturally the Boxcar Children volunteer to help. Then someone steals the shop's advertising brochures and tries to convince people that the shop is closing. When a valuable old guest book signed by the Prince of Wales disappears, along with a customer's wallet, the Boxcar Children investigate.