I kept Madman close at hand as we descended into the depths of the Library, and found Sinner at his usual place in the Research Section, sitting alone and poring over an old leather-bound volume. Tall stacks of books led off in every direction, like a literary maze, and the air was heavy with that distinctive old-book smell. The lighting was clear and distinct but never overpowering, and there were signs everywhere admonishing silence! Discreet signs also pointed you in the direction of books on every subject under the night, some of them adding pointedly at your own risk. Scholars sat at study at their separate desks, ignoring each other, immersed in their work, as devoted in their attention as old-time monks in their cells. I headed straight for Sinner, down the narrow book-lined aisles, Madman ambling along behind me. Sinner looked up as I loomed over him, and nodded thoughtfully. He was a short, compact, and very neat man in his mid forties, looking very much like a civil servant doomed always to be passed over for promotion. Middle-aged, middle weight, almost anonymous. But as his eyes met mine, his gaze was unnervingly bright, and his smile was actually disturbing.

Sinner had been around, and it showed. When he finally spoke, his voice was soft and polite.

"Well, well, John Taylor. I had a feeling I'd be seeing you today, so I just sat here, reading an old favourite, and waited for you."

I looked at the book open on the table before him. It was a Bible, the old King James edition. I raised an eyebrow.

Sinner smiled. "As a wise man once said, Looking for loopholes."

All around us, people were getting up, gathering up their books and papers, and heading for the exit. It could have been Madman's presence, or mine, or perhaps the two of us and Sinner were just too worrying to bear. I couldn't honestly say I blamed any of them. A handful of really hard-core scholars held their ground, hunched protectively over their learned tomes, determined not to be driven off. You have to be pretty tough-minded, to be a scholar in the Nightside. Madman strolled off through the stacks, and the spines of the books on the shelves rippled, changing shape and texture as he passed, affected by his proximity. I had to wonder what new information those transformed books held now; and if I were to take them down and open them, would I find nonsense and gibberish, or perhaps awful wisdom and terrible secrets? I decided I didn't want to know, either way.

And then I was distracted as a lovely young thing came tripping out of the stacks, hugging a tall pile of books in her arms. She was a tall blonde teenager in an English public school uniform, complete with starched white blouse, black miniskirt and stockings, sensible shoes, and a straw boater perched on the back on her perfect head. She was bright and cheerful, heart-stoppingly pretty, far too shapely for her own good, or anyone else's, and moved with all the unrealised elegance of youth. She had a pink rosebud mouth, and eyes so dark they seemed to fall away forever. I stood up straighter and pulled my stomach in, but she flashed me only the briefest of smiles before swaying past me to put the books down on Sinner's desk. I suddenly realised Madman's sound track was playing 'Tubular Bells."

"Allow me to introduce you," said Sinner, in his soft patient voice. "This is my girl-fiend. The demon succubus I fell in love with, all those years ago. I have no idea what you see when you look at her, because it is her nature to appear to everyone as the image of what they secretly most desire."

I wasn't sure if I liked what that said about me. Too many St. Trinians films in my impressionable youth, I suppose. I nodded and smiled politely to the succubus, who pouted her lips briefly as she sat on the corner of Sinner's desk, crossing her long legs to show them off. I had to wrench my gaze away. The pheromones were so thick on the air you could practically see them. It occurred to me that Sinner hadn't said what she looked like to him. Madman wandered back, gave the girl a hard look, shook his head, and wandered off again. I really didn't feel like asking what he might have Seen.

"These are the books you wanted, Sidney," said the succubus, in a rich smoky voice. "Anything else you want, just ask." She arched her back prettily, so that her breasts thrust out against the starched blouse. My mouth was very dry, and I could feel my heart heading for overdrive.

"Her name translates from the original Aramaic as Pretty Poison," Sinner observed calmly. "There are some quite specific verses about her in the Dead Sea Scrolls, none of them complimentary. In the War against Heaven, she killed more than her fair share of angels, and even she doesn't remember how many men she destroyed as a succubus, in her war against Humanity. Watch your manners around her, and never turn your back on her. I love her dearly, but she's still a demon. And by the way—she's the only one who gets to call me Sidney."

I nodded respectfully to the succubus. "How is it that thou art out of Hell?"

Pretty Poison shrugged charmingly. "I couldn't believe that any mortal could truly love me, knowing what I am. Want me, yes, that is my function, to tempt the sinner into damnation, to throw away his immortal soul for the transitory delights of the flesh. But actually to love me, as Sidney did, even knowing the truth, even in the depths of the Inferno; that was a new thing, even in my long existence. So I came back up, out of the Pit, to be with him. Ostensibly I am here as an agent of Evil, to tempt and corrupt him again, so that the Devil can rightly reclaim his soul. But actually, I came back to be with Sidney, to try and understand this thing called ... true love."

"So you say," I said. "But then, to paraphrase another great thinker, you would say that, wouldn't you?"

She looked at me, still smiling, but her eyes were cold, cold. "Did you ever let your lover see the stranger in your soul? All the dark, petty, hidden things you never admit, even to yourself? Did you ever bind yourself utterly to another person, even in the hottest fires of the Inferno? My Sidney did. I have never known such a thing before. There is no love, in Hell. That's why it's Hell. I need to know why he feels the way he feels about me. I need to understand, even if I don't know why."

"But you've known so many men," I said.

"Oh yes," said Pretty Poison. "You have no idea how many, and none of them ever meant a damned thing to me. They said they loved me, here on Earth, but down in the sunless lands they all sang a different tune. They would have betrayed me a hundred times over, for just one more moment of life and light. I never mattered a damn to any of them. Sidney ... is different."

"Pretty Poison was the only one of her kind not to take part in the recent angel war over the Nightside," Sinner said mildly. "Because I asked her not to. Make of that what you will. Now, word travels quickly in the Nightside. And the word is, you've been hired to investigate the true beginnings of the Nightside. By no less a Being than the mercurial Lady Luck herself. You do mix with the most interesting people, John. I have to say, the true nature and purpose of the Nightside is a mystery that has long fascinated me. Do I take it you wish me to accompany you on this most dangerous of quests?"

"Got it in one," I said. "With you and Madman as human shields, I might get through this case alive after all. If I can drag you away from your vital researches, of course..."

Sinner closed the Bible and drummed his fingers on the cover. "My only hope of ever getting into Heaven lies in doing good deeds," he said flatly. "And I mean really impressive, major good deeds. I think keeping you alive in the face of all the really nasty Powers and Dominations who will undoubtedly try to kill you should qualify as good deeds above and beyond the call of duty."