London's underworld is no place for a young woman, even one who is strong, smart and part automaton like Mila. But when master criminal Jack Dandy inadvertently breaks her heart, she takes off, determined to find an independent life, one entirely her own. Her search takes her to the spangled shadows of the West End's most dazzling circus.

Meanwhile, taken captive in the Aether, Griffin King is trapped in an inescapable prison and at the mercy of his archenemy, The Machinist. If he breaks, The Machinist will claim control of the Aether, and no one in either world will be safe.

To defeat The Machinist for good, Griffin will have to confront his greatest fear and finally come face-to-face with the destructive power he wields.