Here's a mystery: why are the marbles in these Chinese Checkers sets so darned ugly? Donny, his sister Mary Grace, their grandmother, and the whole Grandma Gang ride again...discovering criminals who are using a senior center as their surprising base of operations! Donny is a sunny and curious boy with Down syndrome, and Mary Grace is his smart and loving big sister. They and the Grandma Gang work together with seniors of all backgrounds to solve a really big crime. As a team, the kids and the Grandmas show the world that the only real disability is not believing in yourself!