Thirteen-year-old Twig, having always looked and felt different from his woodtroll family, learns that he is adopted and travels out of his Deepwoods home to find the place where he belongs.

Apprenticed to the Most High Academe of Sanctaphrax, a floating city of scholars, gossip, and treachery, fourteen-year-old Quint runs increasingly dangerous errands, which eventually bring him to a place of gruesome monsters that threaten his life and those of his friends.

In his continuing adventures, Twig, now sixteen years old, joins the crew of his father's sky pirate ship and embarks on a dangerous mission to collect the powerful stromphrax, a substance that purifies water and also prevents the city of Sanctaphrax from floating away.

Fleeing from the ruins of New Undertown, Rook Barkwater and the librarian knights and Felix Lodd and his banderbear friends must lead the escaping population to a new life in the Free Glades.

Quint finally begins his training at the Knights Academy, Maris adjusts to life in Undertown, and Sanctaphrax shivers in anticipation of a legendary storm, while a storm of a different kind brews between sky-scholars and earth-scholars.

"Cade Quarter is on the run - wanted for the crimes of an uncle he has never even met. With nowhere else to go, he sneaks onto the Xanth Filatine, a forbidding skyship bound for the city of Hive. But he is soon forced to abandon ship for the harsh lands of the mighty Deepwoods. Cade must build a new life amongst flesh-eating bloodoak trees, fearsome goblin tribes and monstrous lake creatures. And most mysterious of all, a strange, half-formed giant...