This idea basically is about the fall of a young cleric. Our heroine is a young cleric, untested in her faith. In order to join her holy order she has to go and investigate rumors of a haunted castle. The peasants and villagers living in the area refuse to give her information or help of any kind, quite obviously terrified of something.
I imagine the cleric as young, innocent, buxom and busty. She could be, however, shy unsure of herself and deep down unsure of her resolve in her faith and her own abilities. She is, despite being eager to prove herself, frankly, unprepared for the horror that awaits in the castle. What she would encounter would be a Vampire. Thousands of years old, an ancient and horrible evil. In his time in the castle, in the world he has grown weary, bored, alone.
The cleric arrives and would end up captured, held at the mercy of this evil she has sworn to combat. He takes great pleasure in tormenting her, wearing away at the fragile armor of her faith, her sanity. I see this involving non/con, rape (but not violent, he would instead be slow, methodical, seeking to turn her own body against her, bring her all the pleasures and guilty sin she has sworn to avow) and attempt to break her will. I see it involving elements of dom/dub relationship between the two as he attempts to corrupt your character so that can break her faith and eventually turn her into an eternal companion, to stand at his side, his immortal slave and pleasure toy to occupy him forever.
So if anyone is tempted by the idea of taking on the role of cleric, please send me a pm and let me know. :)