Neverwhere by Neil Gaiman

Under the streets of London there’s a world most people could never even dream of. A city of monsters and saints, murderers and angels. This is the city of the people who have fallen between the cracks. A single act of kindness to a ragged girl he finds injured on the street catapults young businessman Richard Mayhew out of his workaday life into a world that is both familiar and threateningly bizarre.

Displaying bold creativity and narrative genius, Neverwhere is a dark, funny, and seductive tale that has become a contemporary literary touchstone.