Fourteen-year-old Ark has the squittiest job on Arborium, the last forested island in the future. A poor plumber's boy, he unblocks toilets in the city where he lives-a breathtaking, mile-high world carved out of the vast upper branches of a giant canopy of trees. Protected by a poisonous shield, he believes his forest kingdom to be the safest place on Earth. But while at work, he overhears a plot between a powerful councillor of the island and a secret spy from Maw, a superpower of glass and steel, that intends robbing Arborium of its wood, a natural resource now more precious than gold. Ark is plunged into danger and soon he finds himself on the run, fighting for his life. Together with new-found friends, he must travel from the highest treetops to the darkest roots of Ravenwood to save his home and his people.