Londoner Zanna finds herself inextricably drawn into a parallel city called ''Un-Lun-Dun.'' With her reluctant friend Deeba also along for the ride, Zanna discovers a city that is as different from her own as anything she could imagine. In Un Lun Dun the garbage is alive, ghosts exist and the government consists of an 'all-knowing' band of Propheseers. However, all is not well in this weird ''ab-city''. An evil force known as Smog is threatening to destroy and devour Un Lun Dun and has ambitious plans to move into Zanna and Deeba's own city. In world that is in desperate need of a hero, can two girls stop the Smog with the help of a half-ghost, a pint of milk and a strangely powerful man who controls broken umbrellas?