Lord Devonshire has won again.

Hector Kingsley, once on the verge of stopping the merciless crime lord's plans, has been driven underground. He is now wanted by the law for crimes Devonshire has committed, and only through the aid of his friends has he remained free. Constables and criminals alike are hunting him, threatening his friends and family. All hope of stopping Devonshire seems lost; it is all Hector can do to stay alive.

Then, as all hope seems gone, an unlikely opportunity arises. Hector is approached by a former employer to carry out an investigation onboard the French embassy, an airship moored over the Thames. Though he faces danger and intrigue on an even more lethal scale, it is a chance that Hector must take, for Devonshire's treasonous plans also involve the floating citadel—and Hector is sure that this time, he must finally defeat his foe or die in the attempt.