Heather Fraser Brainerd 
Shadows of New York [EPUB ebook] 

What do you do when your view of the world gets turned on its head? Eleven-year-old Josh Cooper is surprised when his new nanny ends up being a dude, but that pales in comparison to how he feels when he learns the nanny, Aiden, is also a werewolf. Aiden teaches Josh about the Imaginary World, even introducing him to his friends Larry Fancypants (a suave-yet-goofy vampire) and Steve Lickerman (a tall-yet-meek leprechaun). This fascinating world seems harmless, until Josh learns of the shadowy wraith that’s stalking New York, attacking creatures and stealing their powers. As werewolves are ideally suited for fighting wraiths, Aiden is called upon to help capture the elusive Mr. Midnight, unintentionally drawing Josh even deeper into the strange and mysterious.