This series follows Tessa Cade, an apothecary who illegally distributes medicine to the poor, and Prince Corrick, who enforces his brother's ruthless laws in a kingdom plagued by a mysterious illness. When the supply of life-saving Moonflower petals becomes dangerously low, the two are forced into an uneasy alliance to uncover political conspiracies and prevent a civil war. The narrative explores the moral complexities of power and the sacrifices required to save a crumbling nation.