The story is of young Rook as he becomes a librarian knight and is pitted against the Guardians of the Night, including Xanth Filantine.

Rook Barkwater lives in the network of sewer-chambers beneath Undertown, in which a society of librarians has established itself, secretly opposing the cruel Guardians of Night.

Rook, a lowly under-librarian, dreams of becoming a librarian knight—one of the select few to travel into the Deepwoods and gather information which may lead to the discovery of the cure to stone-sickness (an affliction which has destroyed the buoyant rocks, making skysailing impossible).

Employing the help of a male shryke, Hekkle, who is friendly to the librarians, the three make their way across the Deepwoods, eventually arriving at the Free Glades.

Rook is then introduced to Twig, the main character and sky pirate from the second Edge Chronicles trilogy, now an old man.

Rook and Cowlquape mourn the end of Twig, who had been struck by the crossbow-bolt of the chief guardian of night, Orbix Xaxis and had decided to go down with his ship.

However, at the last minute, Twig's caterbird, who had sworn to watch over him for always, catches him and flies towards the rejuvenating waters of Riverrise.