You know by now what a woman is capable of.

Caroline is home with her father and the woman she loves—but with the Leviathan still unaccounted for, such peace can only be temporary. Soon, the mysterious Mr. Smith is asking for her aid once more: one of the Mastersons' conspirators has been murdered, and the only clue lies in a painting that was last seen in Medby. Meanwhile, Jo has worries of her own, as her affianced sister wants assurances she cannot give—not without denying her very self.

With her arrival in London marked by a second murder, Caroline finds herself once more drawn into a world she wanted to forget. Aided by old friends and new, she and Jo search for the painter, while staying out of reach of Jo's sister's powerful fiancé. But soon they suspect that darker forces are behind the murders, involving not only the painter but his young, pretty wife ... and an imaginary land called Arcadia.

As Caroline and Jo struggle to both stop the murders and protect the life they've made for themselves, they find a new conspiracy is just beginning ... and their choices will come at a price greater than either imagined.