Roofworld - Christopher Fowler

High above London, on the rooftops of the city, lives a secret society of misfits governed by a bizarre code of honour. It is a world known to only a few people on the streets below - until the murderous battle for its leadership breaks out. As the Roofworld fights to kept the powerfully evil Chymes and his occult-worshipping followers at bay, Robert Linden and Rose Leonard, two innocent outsiders, are drawn into a twilight, dangerous world. They face far greater terrors than they could have imagined.

And the battle is on for the ultimate prize - London itself.