It's 1909 and Rose Moriarty—teenage daughter of Sherlock Holmes' greatest enemy—has made a name for herself fighting monsters and solving crimes. But that was before Rose met the one mystery she couldn't solve: the disappearance of her headmistress. Now, her school has shut down, her classmates have scattered, and Rose is on her own.

On the very day Rose receives word that an old friend is dying, the shadowy Count Christoph and his ward Clara show up at her door. Rose has already figured out why they're here (to hire her) and what's in their bag (an ancient orb with incredible powers), but questions remain: Can Rose convince these strangers to help save her friend's life? What are the grotesque, bug-shaped stalkers that plague their every step? And how can Rose pursue this adventure while avoiding a particular boy from her childhood? The only thing certain is that Rose is no longer alone, because danger forges strange alliances . . .

. . . and Professor Moriarty wasn't the only famous villain to have a daughter.