Buster Is Not a Bad Dog — Katherine Applegate

Mouse lives in Dogtown, a shelter for real dogs and robot dogs, where the kibble is plentiful, and the rafters hide a secret community of mice. His unlikely best friend is Buster, a big-hearted real dog who attracts trouble like a burr to fur.

Determined to help Buster find his forever home, even if means losing his best pal, Mouse embarks on a bold quest with three of Dogtown's “unadoptables”: Buster, Stewie--a huge, lovable dog whose ex-owner said he was mean, and Smokey--a robot dog hardwired with a smoke alarm he can't control.

But Mouse is just a mouse, and the world is big and complicated. How's a little guy supposed to find homes for the dogs he loves?