Hidden in the depths of eighteenth-century London, a secret apothecary shop caters to an unusual kind of clientele. Women across the city whisper of a mysterious figure named Nella who sells well-disguised poisons to use against the oppressive men in their lives. But the apothecary's fate is jeopardized when her newest patron, a precocious twelve-year-old, makes a fatal mistake, sparking a string of consequences that echo through the centuries.