In this series debut, Maggie Sinclair tracks down a dognapper and solves a mystery about the noises in the walls of her Brooklyn brownstone apartment building. The 12-year-old heroine, who shares a middle name—Brooklyn—with her twin brother, Finn, is juggling two dogwalking jobs she’s keeping secret from her parents, and somehow she attracts the ire of the dogs’ former walker. Maggie tells her story in the first person—she’s self-possessed and likable, even when her clueless brother invites her ex–best friend, now something of an enemy, to their shared 12th birthday party. Maggie’s attention to details helps her to figure out why dogs seem to be disappearing and why there seem to be mice in the walls of her building, though astute readers will pick up on the solution to at least one mystery before Maggie solves it. There’s a brief nod to Nancy Drew, but the real tensions in this contemporary preteen story are more about friendship and boy crushes than skullduggery. Still, the setting is appealing, and Maggie is a smart and competent heroine whose personal life is just as interesting as—if not more than—her detective work. (Mystery. 10-13)