London, June 1814: On a day out in Hyde Park to celebrate the peace treaty with France, Mary and Jane are less than charmed by their brother Charles’s courtship with a girl from the local cheese shop. When Miss Winnet Davies is not swooning from the heat, she’s imploring Charles to buy her a pretty dress. But he hasn’t a tuppence—nor have they, as their father, philosopher William Godwin, is facing the prospect of debtor’s prison.

When a constable arrives at the Godwin home the following day, looking for Charles, Mary and Jane learn that the lifeless body of Miss Davies was found hanging from a tree branch and an examination revealed she was with child. Their stepbrother has gone missing.

Inclined toward morbidity, Mary assumes he too is dead, but her stepmother admonishes her and insists the sisters find their brother. Before they can search, a terrifying Bow Street Runner named Fisher calls and announces his intention to court Mary. Even if she wasn’t passionately infatuated with married poet and radical Percy Shelley, she is horrified by the massive Bow Street Runner’s plan.

Despite this, to find their brother and clear his name, Mary and Jane alternately enlist the help of the experienced and intimidating Fisher and Shelley himself, who is as enticed by the opportunity to be close to Mary as he is intrigued by the mystery. But the unfortunate shopgirl is only the first to die, and soon the sisters and Shelley face a merciless quarry who will do anything to silence them. . .