London is steaming under a summer of filthy heat and sudden storms - and Detective Nick Belsey, of Hampstead CID, is trying to stay out of trouble.

But then somebody sets him a riddle. How does a man walk into a dead-end alley and never come out? How does he disappear?

And then reappear - to snatch a girl, to dump a body beneath a London skyscraper, to send Belsey a package of human hair.

The answer lies underground, where the secrets degenerating beneath the city's sickly glitter are about to see the light of day.