Picking up shortly after the end of Soulless, the second book finds capable heroine Alexia Tarabotti now Lady Alexia Maccon, newly wed to Lord Connal Maccon, who just happens to also be a werewolf and the chief investigator of supernatural crimes and mysteries in a Victorian England where “the supernatural set” has been integrated into regular society.
Which is when we learn that Alexia is not just a plucky spinster with an interest in the supernatural. She is, herself, supernatural, or rather preternatural — soulless, a rare type of person whose “power” is to render all supernatural beings perfectly normal for as long as she maintains physical contact with them. This is, we quickly learn, a Victorian London slightly different from the one we may remember from history.
Seattle inventor Leviticus Blue is commissioned to create a new machine to speed up the process of digging for gold. The result of his tinkering — The Boneshaker — seems promising until its test-run destroys several blocks of Seattle and penetrates into a deep down reservoir of toxic gas that turns people who breathe it into shambling, hungry “rotters.”