In the great turbine hall of Tate Modern a security guard wandering late at night, torch in one hand, radio in the other, thought he heard something flap up in the high, dark ceiling. He shone his torch up and for a second imagined he could see great leathery wings and hear the scrape of claw on iron. But as this seemed so unlikely, he shook his head and, cursing pigeons under his breath, continued with his patrol.

Behind him a single crumpled piece of paper drifted, swaying in its descent through the still night air.

THANK YOU FOR VISITING TATE MODERN. YOUR FEEDBACK IS IMPORTANT TO US. PLEASE RANK THE FOLLOWING ASPECTS OF YOUR VISIT FROM ONE TO FIVE, AND WRITE ANY OTHER COMMENTS IN THE SPACE BELOW.

In the "Any other comments" box, a careful, neat hand had written: I especially enjoyed the current exhibition on street art in the 21st century, although thought that the curator's interpretation of Two Men, One Stick" was over-laboured. The toilet facilities are clean and pleasant, but the cafe is, I feel, very overpriced and doesn't sell pigeon. Many apologies for the broken skylight; I have left some money and the number of a very professional glazier trained in safe working at heights by the till. Yours faithfully, Sally.

When the note was found during the morning shift, it was dismissed as something of a joke. Then again, someone had broken the skylight above the finance office. Again. And not from the inside.

In Coffee Unlimited, finest coffee within a good five yards, the door opened on an unexpected customer.

"Sharon!" squealed Gina, dropping her tray to run and hug the woman who stepped inside. "Babes, I've been so worried about you when you didn't come in for work, and then when you stopped answering the phone, and there was all this stuff on Facebook and-"

"Sharon?"

She turned. Mike Pentlace, erstwhile employer, iPhone still glued to his hand in a way that made Sharon wonder if, in fact, he'd had an industrial accident, stood there, flushing to the roots of his hair.

"I assume you're here to buy a coffee, yeah?" he asserted. "You can't think you've got a job here any more. Sorry, yeah, but your behaviour has been outrageousutterly outrageousand I always said you had a bad attitude, yeah, but now I see just how bad it was, yeah, so don't think you can come in here and just beg for your-"

"Mr Pentlace," Sharon cut in, "let me put your mind at ease. I am not here to ask for a job. In fact, asking for a job from you is probably the last thing I would ever do on the planet ever, after eating boiled cockroaches, learning to juggle a chainsaw and doggy-paddling in an oil slick.

"The thing is, Mr Pentlace sir, your shop sells the worst coffee in north London and you're the worst manager I've ever met, and even if you paid me a million quid I wouldn't wanna work for you, because a million quid isn't enough to buy comfort from all the bloody grief you give, albeit on a habitual rather than personal basis.

"And I can seecourse I can seethat you're actually a frail little man with deep-seated self-confidence issues which manifest as a flagrant abuse of power, a bullying aggression and a reflexive sense of righteousness. And I really think, Mr Pentlace sir, that you should look at joining a self-help group in order to learn how to be more at one with yourself, and then maybe you can cope with being more at one with everyone else. Something like t'ai chi, perhaps. Or knitting.

"Either way, I figured you'd wanna know that I officially resign because, at the end of the day, working for you just isn't worth my time. I can do so much more. Goodbye, Mr Pentlace. I hope you can find a group willing to take you on."

So saying, Sharon walked away.

This time she remembered both to open the door and close it behind her.

Night settled over London.

One place where it didn't settle as thoroughly as it might have wanted to was the scaffold-encrusted remains of St Christopher's Hall. Lights burned through the brand-new windows, chairs scraped across the fresh plastic covering on the floor, and the smell of tea was almost as unignorable as the noise of gossiping voices from within its walls.

"So what kind of exorcism do you do, Chris?"

"I believe in the psychological approach. It seems to me that if the souls of the departed aren't moving on, then it's almost certainly because they have issues they need to resolve. The book, bell and candle business is very Middle Ages; I've studied Freud and firmly believe that his essential principles can be extended into the nether realms."

The sound of a teaspoon being rattled against a teacup bought the meeting to order. There was a scraping of chairs, a folding of wings, a relaxing of talons, a hiding of fangs, a lowering of bristles and a diminishing of intense magical auras.

The sound of a throat being cleared.

A chair pushed back.

The owner getting to her feet.

"Hi there." Sharon's voice rang out into the hall. "It's so good to see how many of you there are here tonight. Before we begin, a few quick notices. While rebuilding of the hall is going well, any contributions to the church's restoration fund are greatly appreciated, and we would ask that everyone stacks their chairs under the dust covers at the end of the session.

"If you are attending Yoga for Magicians on Tuesday evenings, can I please remind you that all clothing must be fireproofed before you are allowed to practise; and Friday night's quiz, Mystics, Mythics and Magic, has been moved to the Ferret and Fishcake on Essex Road, owing to a clash with karaoke night at the original venue.

"Also, the Society of Friendlies will be handing out leaflets tonight. Their temporary temple will be based in the former Roger's Eel Bar until a new tenancy can be agreed elsewhere, and I'm sure we'll all want to attend their first-service drinks and nibbles. There is also a memorial service for Edna the following Friday. I know many of you have expressed a desire to contribute to this occasion, so Rhys here is going to start a kitty, and once we see how much we collect we'll buy some flowers, or if we have more than that, Rhys may look at buying something better, something that Edna would have liked. I'm sure we all miss her and remember her fondly. If there's no other business, then let me all welcome you to this meeting of Magicals Anonymous. My name's Sharon..."

"Hello, Sharon!"

"... and I'm a shaman."

In the streets outside, a shadow moved across a wall and settled down beside the hunched-up shape of a man in a grubby coat sheltering from the drizzle.

"Oi oi," said the shadow.

"Wotcha," said the man.

"You gonna sit outside or you going in?"

"Don't really know what I'd say," admitted the man. " 'Hello, my name's Matthew Swift. I've been dead a few years now but actually, I think I'm okay'?"

"But are you okay?" countered Sammy. "Only you look like you've been dragged through a cheese grater, and you're sitting out in the rain. I don't need to be the second greatest shaman what ever walked the bloody earth to draw a few conclusions, you know."

"Sammy..."

"Yeah?"

"About your people skills..."

"Screw 'em."

"No, but really."

"I'm a frickin' goblin!" Sammy shrieked. "Jesus, if that doesn't buy you a few perks then what's the friggin' point?!"

"Have you ever considered, though," suggested the sorcerer, "how goblins could, in fact, be cute?"

"Cute?" Sammy spat the word, which was promptly chased by a ball of greyish spittle.

"Well, you're small, you're occasionally furry, you've got these big eyes and a kinda button nose. If you got over the poor body hygiene and the rending of your enemy's raw flesh with your teeth, you could have serious market potential."

"Up yours, sorcerer!"

"That's what everyone says," he conceded.

They loitered, watching the lights moving within the scaffolded hall.

Swift said, "I'm in serious shit, Sammy."

"Like that's new."

"No, but I mean... serious shit. I've been getting lucky for a while, pulling favours, sacrificing... sacrificing things I shouldn't have sacrificed, things I didn't have the right to give away. Making compromises. Sooner or later, my luck had to run out."

"Still here, ain't you?"

Swift sighed, pinching the top of his nose. "That's just it," he muttered. "I'm still here by the skin of my teeth. And now... there's something coming, Sammy. Something... moving beneath the streets. I don't know what it is. I can't... I can't name it, can't see it. And if I can't see it I can't fight it, and that scares me.

"But we can feel it moving. There are whispers, shadows at our back, and we look over our shoulder all the time now. All the time we're on guard and we don't know what it is. I think something's coming. Coming for me. And I don't know how to stop it."

Sammy sucked a judicious lungful of air through his crooked teeth.

"Well, then," he said, "in my professional and highly trained opinion, you're kinda stuffed, ain't you?"

"Thanks."

"You gonna sit there moping or you gonna do something about it?"

Swift hesitated. Then a slow grin spread across his face. "Well," he said with a half-hearted shrug, "no harm trying, is there?"

Time passes.

Sharon sits in the entrance to an office.

There is a small collection of magazines on the table in front of her. They have tag lines such as: THE PERFECT FACIALWHAT WORKS FOR YOU?

and: OUR DREAM CYCLING HOLIDAYNIGHTMARE.

The door to the office opens, and a woman dressed all in black, with a high collar and long sleeves, sticks her head out and beams at her.

"Hi there!" she exclaims, and her gaze is a lighthouse on a foggy night, her smile dazzling and white, her hair bright auburn and her handshake warmer than spring after a long winter. "I'm Kelly, I'm Matthew's assistant here at Harlun and Phelps? You must be Sharon, yes? I love your work, just love it, really, everything you've done, it's so marvellousI hope you haven't been waiting long?"

"I, uh... no?"

"So glad, so glad," Kelly sang out, sweeping Sharon through the door and into the office beyond. It was, Sharon briefly noticed, a bombsite. Paper on the floor, paper on the desk, and paper pinned to the walls, on which more paper had been pinned bearing messages such as: You really have to deal with this Mr Mayor!

Followed by a reply in another hand: How about carpet-bombing?

Sat amid this scene of destruction, as best he could considering his chair was also covered in paper, was Matthew Swift, with his head buried in a report.

"Kelly!" he barked before realising that his assistant was already back in the room with Sharon herded before her.

"Oh," he added. "Yes, right, of course. This," he waved the report at the woman in black, "is a pile of horse manure and I can't be buggered, okay?"

"Absolutely, Mr Mayor. Shall I file it under M for manure or B for buggered?"

"You!"

Sharon realised that Swift's finger was directed at her. "You desperately want to have coffee, don't you?"

"Actually, I had-"

"Good! Let's get out of here."

They had coffee.

Sharon felt guilty about hers, as it was her second in an hour. But then Swift was buying, and who was she anyway to argue with the Midnight Mayor?

She sat in a padded chair which leaned too far back while being simultaneously too close to the table, and waited for Swift to collect his order from the counter. Men and women in suits flowed around them, busy busy busy at the height of the day. Sharon half-closed her eyes and whispered under her breath, "I am beautiful, I am wonderful, I have a secret, the secret is-"

"What the hell is that?" demanded Swift, plonking himself down opposite her like a duck onto ice.

"What? What's what?"

" 'I am beautiful, I am wonderful, I have a secret.' I've heard it somewhere before."

"Oh," mumbled Sharon, flushing crimson. "It's uh... it's this secret, the secret to being confident and comfortable in yourself, I mean. It's like a life-coach thing, only you can teach yourself and that. Whenever you're worried or stressed or don't feel confident or anything, then you can say it and you'll feel, you know, better."

"Better?" queried Swift, as if this was a concept he couldn't quite handle.

"Yeah."

"Because you're... beautiful, wonderful and have a secret?"

"Uh... yeah."

"But... but... what exactly is your secret?"

"Oh that's easy. The secret is me."

A silence followed, punctuated by the sound of the Midnight Mayor slurping his coffee. "Ah," he said, when it was clear no more was going to be offered. "Well." Then, as if the words could no longer restrain themselves, "But that's total bollocks!"

"Um... well, it's, uh... it's..." Somehow everything Sharon wanted to say wasn't quite happening. She sat up a little straighter, surprise showing on her face. "Actually," she declared, "it really is."

"Oh good."

The Midnight Mayor cleared his throat as if he intended to project an air of authority. "So, Sharon," he ventured, "how are you?"

"What?"

"How are you? It's something polite that people are supposed to ask on this sort of occasion."

"What sort of occasion?"

"Well... you know, professional meetings."

"Is that what this is? A professional meeting?"

"Of course it is! I bought coffee! With money! Which I had to sign for and everything!"

A moment of sympathy passed over Sharon's features. "Actually, I've been kinda thinking, what with me being a knower of the truth and that... Do you like being Midnight Mayor?"

"I think it's a question of options," replied Swift primly. "If you're asking 'Would you rather be Midnight Mayor than, say, a smear of coagulating blood on some street corner?' well then I love it. Somehow, in all the excitement, those two seemed to be the only options. Too late to do anything about it now, anyway. Besides! We're not here to talk about me; we need to discuss Magicals Anonymous."