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.