Thalia, Princess of Agripa, has spent the last four years hunting her ex-lover, Cassius- the man who shattered her heart and betrayed her kingdom by becoming a Vampyr. Vampyrs and humans have had a tenuous past since Thalia's father and sister were murdered thirteen years ago. But with Agripa's ore supply -the lifeblood of human cities- running out, Thalia's mother strikes a desperate and dangerous deal: Thalia will marry a Vampyr prince in exchange for their ore. Thalia is blindsided by the arrangement- and horrified to find Cassius, now serving as the prince's Hand, is the man tasked with bringing her to the Vampyr kingdom safely. To save her people, she agrees to the marriage: but plans to dismantle the Vampyr kingdom from within by killing the prince. The Vampyr court is rife with danger and secrets, and Cassius is always watching. When a monstrous new threat emerges, Thalia realises the safety and security of their world is far more fragile than she ever believed. Caught between duty and desire, Thalia must grapple with her feelings for Cassius and decide if she will fulfuill her duty to the human crown or embrace the darkness within herself to protect both realms.