Andrew Peterson 
Monster in the Hollows [EPUB ebook] 
(Wingfeather Series 3)

Janner, Tink, and Leeli Igiby, the Lost Jewels of Anniera, are hiding from Gnag the Nameless in the Green Hollows, one of the few places in the land of Aerwiar not overrun by the Fangs of Dang. But there’s a big problem. Janner’s little brother — heir to the throne of Anniera — has grown a tail. And grey fur. Not to mention two pointed ears and long, dangerous fangs. To the suspicious folk of the Green Hollows, he looks like a monster. But Janner knows better. His brother isn’t as scary as he looks. He’s perfectly harmless. Isn’t he?