Andrew Elliott, Earl of Hartland, is no stranger to scandal. A notorious rake and eccentric genius, he fights crime in armor of his own design and celebrates his achievements with the merriest of widows. What the ton doesn't know is that Hart has received a warning: danger is heading for London and it's looking for Sarah Shipton.

Sarah discovers the bookshop her mother owns is failing and they will have nothing to live on when the month is out. So when the Earl of Hartland offers for her, she agrees to the marriage. But marrying Hart throws Sarah from the frying pan of imminent poverty into the fire of a world filled with science and peril she never knew existed.

How will Sarah cope with the knowledge that someone wants her dead? Can Hart keep her safe from a person hell bent on her destruction?