Hush Little Baby (Vintage Paperback) by Caroline B. Cooney

When Kit Innes’s frazzled ex-stepmother, Dusty, leaves her with an unnamed baby boy and a lot of questions, she’s not sure what to do. She’s doesn’t know if the adorable child is even Dusty’s, or if she plans on returning. But when an angry, frightening man comes looking for the baby, Kit decides that the most important thing is to keep him safe—at all costs.

With the help of her maybe-boyfriend, Rowen, and his little sister, Muffin, Kit is determined to figure out what’s really going on. But as they attempt to return the mysterious baby to wherever it is he belongs, they discover that he’s part of something that could put them all in incredible danger . . .