A couple of years ago, I red this amazing story about a incubus who captured a women and took her with him to his castle to eventually kill her. However, he decided against this. Later he found out she was some sort of special angel(?), who had some mysterical power over demons, because she could turn their sins against them and amplify them. Of course, this story was accompanied by some graphic BDSM descriptions
Oh, and the demon had to prevent other demons from knowing her true nature, as they then would surely kill her.
Anyone any idea what the title of this story was, and where I could find it? I would love to read it again, and this time also the ending