Neil Gaiman's Neverwhere

There are two Londons. London Above is our 'normal' world, and London Below, deep underground, is where the Black Friars and the Hammer Smith live alongside the rat-speakers, and the Earl's Court forever travels the Circle line. Now, Richard Mayhew's normal life will disappear as he's plunged into London Below, thanks to a young streetkid called Door, herself on the run from a deadly plot. Can they survive? Not if Richard's nightmares about crossing Night's Bridge come true.