In the ninth book of the Calendar Mysteries, an early chapter-book mystery series featuring the younger siblings of the A to Z Mysteries detectives, Bradley, Brian, Nate, and Lucy have taken care of the first-grade class hamster, Goldi, for the summer. But on the first day of school, when they plan to bring her back, Goldi is missing! In place of her cage is a green-and-orange sneaker key chain. Soon, the kids spot green-and-orange sneakers all over Green Lawn. And they find out other things have been disappearing around town, too. Can the four friends track down the sneaker sneak and get Goldi back?