Free Dance in the Dark by Megan Derr

"Always in absolute dark; he seems to have some sway over that, as well.
    "I see," Ontoniel said, brows lifting. "That … sounds only like a creature that does not actually exist. Even abnormals have their myths and legends. Every race has its fictional monsters to explain what cannot otherwise be explained or to romanticize the truly frightening and make it easier to bear. What you describe sounds like a legend, a being from another plane, one who can move between planes with impunity."
    Which was practically impossible. Once moved across the planes, creatures tended to stay put, or remain only for a brief stay. One classic example was the dream plane: those who entered it only stayed for a brief time. But those who dwelt in the dream plane, succubi and the like, never left it.  Hell was another well known example: demons left, summoned by those who would harness their power. But once out of hell, they rarely went back. Angels, too, were often pulled from their plane and given corporeal form.
    Precious few were the abnormals who could move across the planes as they chose. They were called Walkers, those who could walk across the planes, and of those only one had ever actually been confirmed—Black Dogs, and very rarely did anyone encounter one of those. Otherwise, it was all myth and legend and unconfirmed sightings.
    So he was being molested by something that did not exist. The thought should irritate him. He did find it frustrating, but like all real mysteries that fell across his path, it only made his blood run hot in thrilled determination.  It was as heady as the kisses he could not forget no matter how hard he tried. "So he is merely clever," Johnnie said aloud. "That was my conclusion, but it still leaves me wondering what he is, that he could pretend to be something that does not exist." Perhaps he would be better served to find the true motive for the man's behavior, and then deduce from there what he was—yes, that was perfect.
    "He is not merely a clever human?" Ontoniel asked. "Give that lot magic, and they can be too crafty for anyone's peace of mind."
    "No, he was too powerful magically to be even a sorcerer; I could smell it on him. He had to be on a par with at least a free imp." He drummed his fingers on his book.
    Ontoniel seemed to hesitate, then said, "What about a half-breed? The history of abnormals is rife with the consequences of mixing races."
    "I am considering that, but his abilities should still be present somewhere and so far I have only found abilities that come close. I suppose I should better factor in how those that are close might alter if crossed with certain other races." His head hurt just thinking about it.
    Silence fell for what seemed several minutes, but could not have been more than a couple, before Ontoniel said, "More than likely, this stranger of yours is an imp or something. However…"
    "However?"
    "However, demons and angels are not the only ones to have forever crossed their planes and settled here. I once heard of a succubus who managed to leave the dream plane and become a normal human. The degree of veracity to the tale, I could not tell you, but in light of such an outlandish description, I suppose the possibility must be considered."
    Johnnie frowned pensively at his book, then quoted, "How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?" He looked up. "I will need better books. Where did you hear this tale of the succubus turned human?"
    "Ages past, and I believe I was still buried somewhere in Eastern Europe at the time," Ontoniel said. "I cannot even recall who told me. More than—" A knock at the door made him pause, then call for the knocker to enter. The door was opened by a servant, who stepped toward them and extended a letter to Johnnie.
    Rostislav? But even as he thought it, Johnnie dismissed it. Letters were not Rostislav's style. If he had any interest in seeing Johnnie, he