Abigail Rook and her eccentric employer, R. F. Jackaby, dive into the cold case, starting with a search for Jenny's fiance, who went missing the night she died. But when a new, gruesome murder closely mirrors the events of ten years prior, Abigail and Jackaby realise that Jenny's case isn't so cold after all, and her killer may be far more dangerous than they suspected. Fantasy and folklore mix with mad science as Abigail's race to unravel the mystery leads her across the cold cobblestones of nineteenth-century New England, down to the mythical underworld, and deep into her colleagues' grim histories to battle the most deadly foe she has ever faced.