The worst thing was I could tell that if I failed to understand, if I couldn't get a fix on that borderline, then I was doomed. And it wasn't just me. Svetlana would die too. She'd get embroiled in a hopeless attempt to save her boss. The entire structure of the Moscow Watch would collapse.

If I didn't get the one thing right.

I went on standing there for a while, with my hand against the dirty brick wall. Digging through my memory, chewing things over, trying to find an answer. There wasn't one. That meant it was destiny.

I walked across the quiet little courtyard to the 'box on stilts'. The Soviet skyscraper made me feel strangely despondent. There was no obvious reason, but the feeling was undeniable. I'd felt the same thing before, in a train passing abandoned villages and crumbling grain silos. The sense of wasted effort. A punch thrown too hard, connecting with nothing but the air.

'Zabulon,' I said, 'if you can hear me . . .'

All was calm. The usual calm of a late evening in Moscow – car engines roaring, music playing somewhere behind the windows, empty streets.

'There's no way you can have covered every single possibility,' I said, speaking to the empty air. 'Just no way. There are always forks in the road in reality. The future isn't determined. You know that. And so do I.'

I set out across the road without looking right or left, ignoring the traffic. I was on a mission, right?

The sphere of exclusion.

A trolleybus screeched to a halt on the rails. Cars braked and skidded round an empty space with me at its centre. Nothing else existed for me now, only that building where we'd done battle on the roof three months before, in the darkness, those bright flashes of an energy that human eyes couldn't see.

And that power, visible to so few, was increasing.

I was right, this was the eye of the hurricane. This was where they'd been leading me all this time. Great. Now I'd arrived. So you didn't forget that shabby little defeat after all, Zabulon? You haven't forgotten the way you were sent down in front of your underlings.

Apart from all his exalted goals – and I understood that for him they were exalted – the Dark Magician harboured another burning desire. Once it had been a simple human weakness but now it had been increased immeasurably by the Twilight.

The desire for revenge. To get even.

To play the battle out all over again.

All you Great Magicians share this, Light and Dark – this boredom with ordinary battle, this desire to win elegantly. To humiliate your opponent. You're weary of simple victories, you've had plenty of those already. The great confrontation has developed into an endless game of chess. Gesar, the great Light Magician, was playing it when he assumed another's appearance and took such delight in taunting Zabulon.

But for me the confrontation still hadn't turned into a game.

And maybe that was exactly where my chance lay.

I took the pistol from its holster and clicked the safety catch off. I took a deep, deep breath as if I was about to dive into water. It was time.

Maxim could sense that this time it would all be over quickly.

He wouldn't spend all night lying in wait. He wouldn't spend hours tracking down his prey. This time the flash of inspiration had been too bright. More than just a sense of an alien, hostile presence – a clear direction to his target.

He drove as far as the intersection of Galushkin Street and Yaroslavskaya Street and parked in the courtyard of a high-rise. He watched the black flame glimmering as it slowly moved about inside the building.

The Dark Magician was in there. Maxim could already feel him as a real person, he could almost see him. A man. His powers were weak. Not a werewolf or a vampire or an incubus. A straightforward Dark Magician. The level of his powers was so low, he wouldn't cause any problems. The problem was something else.

Maxim could only hope and pray that this wouldn't keep happening so often. The strain of killing the creatures of the Dark day after day wasn't just physical. There was also that terrible moment when the dagger pierced his enemy's heart. The moment when everything started to shudder and sway, when colours and sounds faded away and everything started moving slowly. What would he do if he ever made a mistake? If he killed someone who wasn't an enemy of the human race, but just an ordinary person?

But there was nothing he could do, since he was the only one in the entire world who could tell the Dark Ones from ordinary people. Since he was the only one who'd been given a weapon – by God, by destiny, by chance.

Maxim took out his wooden dagger and looked at the toy with a heavy heart, feeling slightly confused. He wasn't the one who'd whittled this dagger, he wasn't the one who'd given it the high-flown name of a 'misericord'.

They were only twelve at the time, he and Petka, his best friend, in fact his only childhood friend and – why not admit it? – the only friend he'd ever had. They used to play at knights in battle – not for very long, mind you, they had plenty of other ways to amuse themselves when they were kids, even without all these computer games. All the kids on the block had played the game for just one short summer, whittling swords and daggers, pretending to stab at each other with all their strength, but really being careful. They had enough sense to realise that even a wooden sword could take someone's eye out or draw blood. It was strange how he and Petka had always ended up on opposite sides. Maybe that was because Petka was a bit younger and Maxim felt slightly embarrassed about having him as a friend, the adoring way he gazed at Maxim and trailed around after him as if he was in love. It was just an ordinary moment in one of their battles when Maxim knocked Petka's wooden sword out of his hands – his friend had hardly even tried to resist – and cried: 'You're my prisoner!'

But then something odd had happened. Petka had handed him this dagger and said that the valiant knight had to take his life with it rather than humiliate him by taking him prisoner. It was a game, of course, only a game, but Maxim had shuddered inside when he pretended to strike with the wooden dagger. And there had been one brief, agonising moment when Petka had looked at Maxim's hand holding the dagger just short of his grubby white t-shirt and then glanced into Maxim's eyes. And then he'd blurted out: 'Keep it, you can have it as a trophy.'

Maxim had been happy to accept the wooden dagger. But for some reason he'd never used it in the game again. He'd kept it at home and tried to forget about it, as if he felt ashamed of the unexpected gift and his own sentimentality. But he'd never forgotten it. Even when he grew up and got married and his own first child was growing up, he'd never forgotten it. The toy weapon always lay in the drawer with the photo albums of the children, the envelopes with locks of hair and all that sentimental nonsense. Until the day Maxim first felt the presence of the Dark in the world.

It was as if the wooden dagger had summoned him. And it had proved to be a genuine weapon, pitiless, merciless, invincible.

But Petka was gone now. They'd grown apart when they were still young: a year is a big age difference for children, but for teenagers it's a huge gulf. And then life had separated them. They'd still smiled at each other whenever they met and shaken hands, had even enjoyed a drink together a few times and reminisced about their childhoods. Then Maxim had got married and moved away and they'd almost completely lost contact. But this winter he'd had news of Petka, purely by chance, from his mother – he phoned her regularly, just like a good son should. 'Do you remember Petka? You were such good friends when you were children, quite inseparable.'

He'd remembered. And he'd realised immediately where this was leading.

Maxim's mother told him that he'd fallen to his death from the roof of some high-rise, though God only knew what he'd been doing up there in the middle of the night. Maybe he'd committed suicide, or maybe he'd been drunk – but the doctors had said he was sober. Or maybe he'd been murdered. He had a job in some commercial organisation that paid well, he used to help his parents and drive around in a good car.

'He was probably high on drugs,' Maxim had said sternly. So sternly his mother hadn't even tried to argue. 'I suppose so, he always was strange.'

His heart hadn't contracted in sudden pain. But for some reason that evening he'd got drunk and killed a woman he'd been trying to track down for two weeks, a woman whose Dark power forced men to leave the women they loved and go back to their wives, an old witch who forced people together and forced them apart.

Petka was gone. The boy he'd been friends with had already been gone for many years, and now Pyotr Nesterov, the man he'd seen once a year or even less often, had been gone for three months. But Maxim still had the dagger Petka had given him.

There must have been some special reason for it, that awkward childhood friendship of theirs.

Maxim toyed with the wooden dagger, rolling it from one hand to the other. Why was he so alone? Why didn't he have a friend beside him to lift at least part of the burden from his shoulders? There was so much Dark all around, and so little Light.

For some reason Maxim recalled the last thing Elena had shouted at him as he was leaving: 'I wish you'd love us, not just take care of us.'

But isn't that the same thing? thought Maxim, mentally parrying the thrust.

No, it probably wasn't. But what was a man to do when his love was a battle fought against Evil, rather than for Good?

Against the Dark, not for the Light.

Not for the Light but against the Dark.

'I'm the guardian,' Maxim said to himself in a low voice, as if he was too fearful to say it out loud. Only schizos talked to themselves. And he wasn't a schizo, he was normal. He was better than normal, he could see the ancient Evil creeping and crawling into the world.

But was it creeping in, or had it already made its home here a long, long time ago?

No, this was madness. He mustn't, he absolutely mustn't allow himself to doubt. If he lost even a part of his faith, allowed himself to relax or start searching for non-existent allies, then he was finished. The wooden dagger would no longer be a luminous blade driving out the Dark. The next magician would reduce it to ashes with magic fire, a witch would cast a spell on it, a werewolf would tear it to pieces.

The guardian and the judge!

He mustn't hesitate.

The patch of Dark moving about on the ninth floor suddenly started moving downward. His heart started beating faster: the Dark Magician was coming, to keep his appointment with destiny. Maxim climbed out of the car and glanced rapidly around him. As usual, some secret thing inside him had driven everyone away from the scene and cleared the battlefield.

Was it a battlefield? Or a scaffold?

Guardian and judge?

Or executioner?

What difference did it make?

The familiar power flooded into his body. Holding his hand inside his jacket, Maxim walked towards the building's entrance, towards the Dark Magician who was coming down in the lift.

Quickly, it had to be done quickly. It still wasn't quite night yet. Someone might see. And no one would ever believe him, the best he could hope for would be the madhouse.

Call out. Give his name. Take out his weapon.

Misericord. Mercy. He was the guardian and the judge. The warrior against evil. And not an executioner!

This courtyard was a battlefield, not a scaffold.

Maxim stopped outside the entrance to the building. He heard footsteps. The lock clicked.

He felt so wronged, he could have howled in horror and screamed curses at the heavens for his destiny and his gift.

The Dark Magician was a child.

A skinny, dark-haired little boy who looked quite ordinary – except for the quivering halo of Dark that only Maxim could see.

But why? Nothing like this had ever happened to him before. Maxim had killed women and men, young and old, but he'd never come across any children who'd sold their souls to the Dark. He'd never even thought about it, maybe because he hadn't wanted to accept that it was possible, or maybe because he'd been avoiding making any decisions in advance. He might have stayed at home if he'd known his next victim would be only twelve years old.