As the London Season of 1877 opens, Lady Margaret Savoy wants nothing more than to be invisible and devour "Penny Dreadfuls" to avoid the cruelty of her aunt and cousin. When she finds a letter from her grandfather warning her about a man called the Poisoner, a powerful crime boss who killed her parents, her wallflower days come to an abrupt end as she falls into a deadly investigation. Literally. Out a window, in fact, and right into the path of Lord Alexander Rocque, a young detective. Alexander offers his assistance-with the Poisoner, and the window-and together they set out to discover the Poisoner's plans. But Lord Alexander has plans of his own. Recently ordered home from the Royal Navy to assist his father, a spymaster for the Crown, with the Poisoner case, Alexander is determined to earn his father's respect by catching the criminal through any means necessary. The perfect tool falls into his lap in the form of Lady Margaret, the Poisoner's next target, but using Margaret to draw out the crime boss has Alexander examining his moral compass. As Margaret learns about her heritage and Alexander uncovers his father's affiliation with the East Indian Company, they discover that their families are not so innocent after all. To stay alive in the Poisoner's game, they must find the key to the dying Opium trade-a key Margaret may, in fact, possess herself. If they don't find it, the Poisoner will escape yet again, but even worse, Margaret will become the next victim.