The owl made a wide circle round the tornado, then flew lower and over our heads. Olga still looked very self-possessed, but her careless emergence from the Twilight showed how agitated she really was.

'Why, what did he do wrong?'

'Nothing really . . . except for being overconfident. He got to know the girl. Then he started pushing things along and that made the twister start to grow . . . and how!'

'I don't understand,' I said, confused. 'It can only grow that way if it's being fed with energy by the magician who summoned up the Inferno . . .'

'That's the whole point. Someone must have tracked Ignat and started shovelling coal in the firebox. This way. . .'

We entered the building that stood between us and the vortex. The owl flew in after us at the last moment. I gave Ilya a puzzled look, but I didn't ask any questions. Anyway, it was clear soon enough why we were there.

An operations centre had been set up in an apartment on the first floor. The heavy steel door, firmly closed in the human world, was standing wide open in the Twilight. Without stopping, Ilya dived into the Twilight and walked through. I fumbled for a few seconds, raising my shadow, and followed him.

It was a large apartment, with four rooms, all very comfortable. But it was also noisy, smoky and hot.

There were more than twenty Others there, including the field operatives and us back-room boys. No one took any notice when I arrived, they just glanced at Olga. I realised that the old Watch members knew her, but no one made any attempt to say hello or smile at the owl.

What could she have done?

'Go through into the bedroom, the boss is in there,' Ilya said briskly, turning off into the kitchen, where I could hear glasses clinking. Maybe they were drinking tea, or maybe it was something a bit stronger. I glanced in quickly as I passed and saw I was right. They were reanimating Ignat with cognac. Our sexual terrorist looked completely knackered, crushed. It was a long time since he'd suffered this kind of failure.

I walked on by, pushed open the first door I came to and looked inside.

It was the children's room. A child of about five was sleeping on a little bed, and his parents and teenage sister were on the carpet beside it. Clear enough. The owners of the apartment had been put into a sound, healthy sleep so they wouldn't get under our feet. We could have set up the entire operations office in the Twilight, but why waste all that energy?

Someone slapped me on the shoulder and I looked round – it was Semyon.

'The boss is this way,' he told me. 'Come on . . .'

It seemed like everyone knew I was expected.

When I entered the next room, I was taken aback for just a moment.

There couldn't be any more absurd sight than a Night Watch operations centre set up in a private apartment.

There was a medium-size magic sphere hanging in the air above a dressing table stacked with cosmetics and costume jewellery. The sphere was transmitting a view of the vortex from above. Lena, our best operator, was sitting on a chair beside it, silent and intense. Her eyes were closed, but when I came in she raised one hand slightly in greeting.

Okay, so that was usual enough. Sphere operators see space in its totality, there's no way to hide anything from them.

The boss was reclining on the bed, propped up with pillows. He was wearing a bright-coloured robe, soft oriental slippers and an embroidered skullcap. The room was filled with the sweet fumes of a portable hookah. The owl was sitting in front of him. It looked as if they were communicating silently.

That was all usual enough too. In moments of exceptional stress, the boss always reverted to the habits he'd picked up in Central Asia. He'd worked there at the end of the nineteenth century and the beginning of the twentieth, first disguised as a mufti, then as a Muslim guerrilla leader, and then as a red commissar, and finally he spent ten years as the secretary of a district party committee.

Danila and Farid were standing by the window. Even with my powers I could make out the purple glimmer of the wands hidden in their sleeves.

A perfectly standard arrangement. At moments like this the headquarters was never left unprotected. Danila and Farid weren't the strongest fighters we had, but they were experienced, and that was often more important than crude strength.

But what was I supposed to make of the last Other in the room?

He was squatting modestly and unobtrusively in the corner. As thin as a rake with sunken cheeks, black hair cut short, military style, and big, sad eyes. It was impossible to tell how old he was, maybe thirty, maybe three hundred. He was dressed in a dark, loose-fitting suit. A human would probably have taken the stranger for a member of some obscure sect. And he would have been half right.

He was a Dark Magician. And a powerful one too. When he glanced briefly at me, I felt my protective shell – which wasn't installed by me – crack and start to buckle.

I took an involuntary step backwards. But the magician had already lowered his eyes to the floor as if to show me that the momentary probing had been accidental . . .

'Boris Ignatievich.' I could hear my voice wheezing slightly.

The boss nodded curtly, then he turned to the Dark Magician, who immediately fixed his eyes on him.

'Give him an amulet,' the boss ordered brusquely.

The Dark Magician's voice was sad and quiet, the voice of someone burdened with all the woes of the world.

'I'm not doing anything forbidden by the Treaty. . .'

'Neither am I. My colleagues must be immune against observers.'

So that was it! We had an observer from the Dark Side in our headquarters. That meant Day Watch had a headquarters somewhere close by, and one of us was there.

The Dark Magician put his hand in his jacket pocket. He took out a carved ivory medallion on a copper chain and held it out to me.

'Throw it,' I said.

The magician smiled gently with the same air of melancholy sympathy and flicked his hand. I caught the medallion. The boss nodded approvingly.

'Your name?' I asked.

'Zabulon.'

I hadn't heard the name before. Either he wasn't that well known, or he was somewhere right up at the top of the Day Watch.

'Zabulon . . .' I repeated, glancing at the amulet. 'You no longer have any power over me.'

The medallion grew warm in my hand. I put it on over my shirt, nodded to the Dark Magician and walked over to the boss.

'You can see how things are, Anton,' the boss said, mumbling slightly, because he hadn't taken the mouthpiece of the hookah out of his mouth. 'There you are, look.'

I looked out the window and nodded.

The black vortex sprouted out of a nine-storey block just like the one we were in. Its slim, flexible stalk ended somewhere around the first-floor level. By reaching out through the Twilight, I could locate the precise apartment.

'How could this have happened, Boris Ignatievich?' I asked. 'This is a lot more serious than a brick falling on someone's head, or even a gas explosion in a hallway.'

'We're doing everything we can.' The boss seemed to think he had to justify himself to me. 'All the missile silos are under our control, the same measures have been taken in the US and France, and they're just being put in place in China. Things are a bit trickier with the tactical nuclear weapons. We're having big problems locating all the operational laser satellites. The city's full of all sorts of bacterial garbage ... an hour ago there was almost a leak from the Virological Research Institute.'

'You can't cheat destiny,' I said guardedly.

'Exactly. We're plugging the holes in the bottom of the ship, and the ship's already breaking in half.'

I suddenly noticed that everyone – the Dark Magician, and Olga, and Lena, and the warriors – was looking at me. I began to feel uncomfortable.

'Boris Ignatievich?'

'You're linked to her.'

'What?'

The boss sighed and took the hookah tube from his mouth. The cold opium smoke streamed out on to the floor.

'You, Anton Gorodetsky, a programmer, unmarried, of average abilities, are linked to the girl with that vile black filth hanging over her head.'

The Dark Magician in the corner sighed softly. I couldn't think of anything better to say than 'Why?'

'I don't know. We sent Ignat to her, and he did a good job. You know he can seduce anyone.'

'But it didn't work with her?'

'It did. Only the vortex started to grow. They spent half an hour together and the vortex grew from a metre and a half to twenty-five metres. We had to call him off. . . quickly.'

I glanced sideways at the Dark Magician. Zabulon appeared to be looking at the floor, but he immediately raised his head. This time my defensive shield didn't react: the amulet gave me secure protection.

'We don't need this,' he said in a low voice. 'Only a savage would kill an elephant to get a small steak for his breakfast.'

The comparison shocked me. But he seemed to be telling the truth.

'We don't require destruction on this scale very often,' the Dark Magician continued. 'At the moment we don't have any ongoing projects that require such a large-scale discharge of energy.'

'I really hope you don't . . .' said the boss, in a strange, grating voice. 'Zabulon, what you have to understand is that if this disaster does happen, we'll squeeze everything we can out of it too.'

The shadow of a smile appeared on the Dark Magician's face.

'The number of people who will be horrified by what has happened, who will spill tears of sympathy with others' grief, will be very great. But there will be more, infinitely more, who will sit with their eyes glued greedily to their TV screens, who will take pleasure in other people's suffering, feel glad that it passed their city by and make jokes about the retribution meted out to the Third Rome . . . retribution from on high. You know that, my enemy.'

He wasn't gloating, the highest-ranking Dark Ones don't react in such primitive ways. He was stating a fact.

'Nonetheless, we're ready,' said Boris Ignatievich. 'You know that.'

'I know, but we are in a more advantageous position. Unless you have a pair of aces up your sleeve, Boris.'

'You know I always have all four.'

The boss turned towards me as if he'd completely lost interest in the Dark Magician.

'Anton, the vortex isn't being nourished by the Day Watch. Whoever created it is working on his own. An unknown Dark Magician of terrible power. He sensed Ignat's presence and accelerated the pace of events. Now you're our only hope.'

'Why?'

'I told you Anton, you're linked. There are three divergences in the probability field.'

The boss waved his hand and a white screen unfurled in the air. Zabulon frowned, he must have been caught by the edge of the energy discharge.

'The first path along which events can develop,' said the boss. A black stripe ran across the white sheet that hung in the middle of the room without any visible means of support. Then it blurred, spreading out in an ugly blot that extended beyond the edge of the screen.

'This is the most probable path. The vortex attains its maximum power and the Inferno erupts. Millions killed. A global cataclysm – nuclear, biological, asteroid impact, a twenty-point earthquake. You name it.'

'And a direct infernal discharge?' I asked cautiously, glancing sideways at the Dark Magician. His face remained impassive.