Hidden under the surface of everyday London is a city of monsters and miracles, where wild train spirits stampede over the tracks and glass-skinned dancers with glowing veins light the streets.
When a devastating betrayal drives her from her home, graffiti artist Beth Bradley stumbles into the secret city, where she finds Filius Viae, London's ragged crown prince, just when he needs someone most. An ancient enemy has returned to the darkness under St. Pauls Cathedral, bent on reigniting a centuries-old war, and Beth and Fil find themselves in a desperate race through a bizarre urban wonderland, searching for a way to save the city they both love.