Ever since Beth Bradley found her way into a hidden London, the presence of its ruthless goddess, Mater Viae, has lurked in the background. Now Mater Viae has returned with deadly consequences. Streets are wracked by convulsions as muscles of wire and pipe go into spasm, bunching the city into a crippled new geography; pavements flare to thousand-degree fevers, incinerating pedestrians; and towers fall, their foundations decayed. As the city sickens, so does Beth—her essence now part of this secret London. But when it is revealed that Mater Viae's plans for dominion stretch far beyond the borders of the city, Beth must make a choice: flee, or sacrifice her city in order to save it.