Acclaimed fantasist Miéville’s first foray into youth literature starts predictably but progresses to match his reputation. The overlong first section, in which two girls (chosen Zanna and sidekick Deeba) travel to UnLondon, a dream-logic London (houses made of obsolete technology; walking bushes; feral giraffes) where sentient smog threatens the populace, will entice imaginations. Unfortunately, it is also too reminiscent of Neil Gaiman’s work (particularly MirrorMask). Zanna fails and has her memory wiped, but Deeba can’t forget their adventures, especially when she discovers the threat is worse than anyone thought. She returns to UnLondon, flouting destiny and distressing all, especially the talking book of prophecy, which becomes highly and comically insecure. Deeba must journey through this truly fantastic world, with no guidance except her own wits. Intrigue with London officials, a half-ghost ally and fighting “unbrellas” all play a role, as does a definite but not heavy-handed message about pollution and the environment. Ultimately, this is a compelling tale of heroism from someone foretold as merely “the funny one,” and a well-evoked dreamscape that readers will embrace. (Fantasy. 10+)