Dark demon - Christine Feehan

Carpathians are an immortal race of beings with animal instincts and the ability to shape shift. Every Carpathian male is drawn to a life mate:
a woman -
Carpathian or human -
able to provide the light to his darkness. Without her, the beast within slowly consumes the man until turning into a vampire is the only option.' Natalya Shonski is a vampire hunter, descended from a revered line of Carpathians known as the Dragonseekers and the most powerful mage in history. She hates and fears both vampires and Carpathians alike and has spent her life fighting them. Carpathian Vikirnoff van Schreider is dangerously close to turning vampire when he discovers Natalya and realises that she is his lifemate.
But Natalya is unlike any other Carpathian he has ever known - dangerous in her own right, she refuses to let him fight her battles, and she infuriates him with her cheerful disregard of his demands.
But a sinister, mysterious power is after Natalya, and Virkirnoff has to convince her not only to trust him with her heart, but with her life as well.