When Richard Mayhew helps a wounded girl on the street, he finds himself beginning a nightmare journey that plunges him into a weird parallel world underneath London. The girl is on the run from two cut-throats who she thinks killed her family. But why are they after her? And now that Richard is involved, will he ever return to a normal life?

Richard Mayhew has fallen into a parallel world that exists beneath the streets of London and he wants his old life back. His only chance is to find Door and the Marquis, who have set off for the Floating Market in search of a bodyguard to protect Door from Croup and Vandemar. But Richard could do with protection himself.