In the depths of eighteenth-century London, a secret apothecary shop run by Nella caters to women seeking poisons for oppressive men. When a young girl makes a mistake, the shop's fate is jeopardized. In present-day London, historian Caroline Parcewell discovers clues to the unsolved murders, intertwining her life with Nella's in a thrilling tale of secrets, vengeance, and female solidarity across centuries.