Tanith Lee 
Vivia 

Vivia, a paragon of youth and beauty, daughter of Lord Vaddix, is alienated from his brutal campaign of violence and fear. Her only solace lies in the secret cave in the bowels of the castle, known only to her and the arcane god whose shrine she believes it is.When plague enters the castle, bringing an orgy of death and destruction, Vivia seeks shelter in this seductive place. Drawn to her innocence and beauty, a presence – Zulgaris – is resurrected who claims her as his own. Wakened to the wonder of the undead, Vivia is granted the secret of eternal life, but she has been betrayed. Her immortality stretches before her like a damnation. Handsome Zulgaris, dark prince, war-leader and alchemist. Is Vivia to be his lover, or his pet? Or, far worse, is she but one more thing to be used in this relentless quest for sorcerous power.