After defeating a clockwork army bent upon regicide, the sorceress Emma Bannon and genius detective Archibald Clare have come to respect each other's skills, despite the fact that magic and logic are usually opposing forces.

So when the Queen asks Emma to track down a missing doctor who holds the key to a deadly new weapon, Archibald's deductive talent may be just what she needs to find the man, before his destructive discovery sets the entire capital city ablaze . . .