The Wingfeather (formerly known as Igiby) children are sailing across the sea, leaving behind their Fang-infested home and hoping to find refuge in the Green Hollows, home of their grandparents and Aerwiar's last Fang-free nation. In many ways, Ban Rona (capital of the Green Hollows) seems like the home Janner has longed for; Fang-free, full of dogs, good food and "bibes" (drinks), with a library, their father's dearest friend, and even their very own ancestral house. The children are enrolled in the local school (the ugly head-mistress being their mother's childhood best friend) where they are trained in Hollish specialties of Sneakery, Dogspeak, and Pummelry Training. For the first time, Nia seems truly happy, even beginning a courtship with a childhood friend, now the Keeper of the Hollows. However, Kal is still a Fang, with deadly claws, a ferocious appetite, and a darkness to fight. Janner struggles to continually sacrifice his own desires to try and keep his brother safe, knowing that his mother's fate is also at stake. The family is still without their father, and his loss is ever more keenly felt. Dangers lurk in the Blackwoods, mysterious misshapen horrors called "the cloven," and one makes its way into Ban Rona, making a strange connection with the Wingfeather children. Janner worries that Gnag the Nameless is at work. And there is something stealing livestock, stirring up the fear and distrust of outsiders that has wormed its way deep into the Hollish folk. There is a monster in the Hollows. Is it Kalmar?