In the sword-and-sorcery Empire of Aoslan, Sophia, a low-ranking scribe, is expelled from the Magic Guild after an unexpected onset of lactation. With nowhere left to turn, she is found by Damian, the all-powerful Shadow Grand Duke—cursed with an ancient dark magic—who purchases her breast milk for the staggering sum of 500,000 gold coins as the sole antidote to suppress his curse. Hunted by her brutal mercenary husband, Sophia flees with her infant daughter into the Duke's impenetrable Obsidian Citadel. Through repeated intimate "treatments," their fates become inextricably entwined. But when the shadows of the past close in and the empire's power struggles erupt, Sophia must awaken the hidden purifying bloodline within her, stand shoulder to shoulder with the Duke against the dark conspiracies of the Imperial Throne and the Holy Church—and rise to become the true mistress of the empire.
