Seraphina Vance, a struggling New Yorker, is drawn into a hidden war between Heaven and Hell when Lucifer Morningstar, the King of Hell, becomes fixated on her. Caught in the conflict, she is turned into a permanently immortal being who must survive on blood, forcing her into a new, unstable existence she never chose. As Lucifer continues to interfere in her life and the celestial war shifts around them, their connection deepens into an inevitable and dangerous love neither Heaven nor Hell can fully stop.