The year is 1946, and Eleanora Fagan is celebrating her seventeenth birthday. Like most girls her age, she's started thinking about boys, dating, and even who she might marry someday. But she was promised to someone long before she was born.

The day Lucifer fell from Heaven, Nora's father, the Archangel Samael arranged the marriage with a secret Covenant formed to maintain the balance between Good and Evil. On Nora's one-hundredth birthday she will marry Azazel the Fallen and their union will prevent the Apocalypse. Azazel meets Nora at her birthday party, and they quickly become friends.

Over the next year, they battle against foes who wish to bring about the end of the world, and the lines between friendship and love blur. The contract that binds them has only one rule they seem destined to break: No sex before marriage. When Nora turns eighteen, she will become a fully mature succubus, and must feed on sexual energy to survive. She has her pick of partners, except Azazel. Can they maintain a platonic relationship for eighty-two years, or will they let the world end in flames?