In the heart of post-war London, a bomb is discovered lodged at a disused station between Green Park and Hyde Park Corner. The bomb detonates, and as the dust clears, it becomes apparent that something has been awakened. Strange half-human creatures attack the workers at the site, hungrily searching for anything containing sugar . . .
Meanwhile, Honoré and Emily are contacted by eccentric poet Randolph Crest, who believes himself to be the target of these subterranean creatures. The ensuing investigation brings Honoré and Emily up against a terrifying force from deep beneath the earth, and one which even with their combined powers, they may have trouble stopping.