Going to throw an idea onto this that needs some developing:
A Vampire Lord leaves the safety of his keep so that he can research a rumor he has heard about the blood of fae. It is his belief that if he can drink from a winged fae that he will gain access to power that is unheard of, eventually making him powerful enough to challenge his dark masters that reside elsewhere in the world. The forest rejects him as the cursed creature he is, but he is unrelenting in his search and eventually finds and captures a human-sized fae woman and feeds off of her. When nothing changes for him, he decides to bring her back to his keep and study her to see if he has done something wrong and how he can fix it. The faerie, unbeknownst to the vampire, has fantasized of dark and mysterious men before, and is seeking his attention sexually despite being treated as a prisoner.