Twelve year old girls Zanna and Deeba are getting seriously worried by the weird things that keep happening to them. After a dark cloud attacks them, they follow a broken umbrella which is somehow managing to move by itself, and find a gap between their home city on London and UnLondon, a weird mirror image of the capital inhabited by creatures and animated objects which have been discarded by London's inhabitants and fallen through to the other world. Quickly, Zanna is recognised as the Shwazzy, or chosen one, beginning a quest to save UnLondon from the Smog - but this is no ordinary fantasy quest, and there are lots of twists and turns on the way, including several deaths and various betrayals.
Un Lun Dun is a glorious romp through a fantastically imagined world which works as both a spoof of conventional stories - I particularly liked Deeba's disgust at finding herself referred to in the book of prophecy as the Chosen One's funny sidekick - and as an exciting adventure in its own right. The scene in which the party are captured by Mr Speaker stood out as particularly imaginative, as did the utterlings - creatures created whenever Mr Speaker opens his mouth, taking shape from each individual word.
With a fantastic heroine, a host of brilliant supporting characters - Jones the bus conductor and Curdle the milk carton standing out for me, with an honourable mention for the binja (ninja rubbish buns) who I'd love to have seen even more of), this is a huge recommendation for all fans of great fantasy. I loved Mieville's world-building and would be really excited if this talented author was to return to UnLondon in the future.