The door didn't open.

That couldn't happen!

In the real world all the locks on the door could be closed, but the Twilight has its own laws. Only vampires need an invitation to enter someone's home, that's the price they pay for their strength and their gastronomic approach to humans.

In order to lock a door in the Twilight, you had at least to know how to enter it.

'Fear,' said Olga. 'Yesterday the boy was in a state of terror. And he'd just been in the Twilight world. He locked the door behind him, and without knowing it, he locked it in both worlds at the same time. Come deeper. Follow me.'

I looked at my shoulder – there was no one there. Summoning the Twilight while you're in the Twilight is no simple trick. I had to raise my shadow from the floor several times before it acquired volume and hung there, quivering in front of me.

'Come on, come on, you're doing fine,' whispered Olga.

I entered the shadow, and the Twilight grew thicker. Space was filled with a dense fog. Colours disappeared completely. The only sound left was the beating of my heart, slow and heavy, rumbling like a drum being beaten at the bottom of a ravine. And there was a whistling wind – that was the air seeping into my lungs, slowly stretching out the bronchi. The owl appeared on my shoulder.

'I won't be able to stand this for long,' I whispered, opening the door. At this level, of course, it wasn't locked.

A dark grey cat flitted past my feet. For cats there is no ordinary world or Twilight – they live in all the worlds at once. It's a good thing they don't have any real intelligence.

'Kss-kss-kss,' I whispered. 'Don't be afraid, puss . . .'

Mostly to test my own powers, I locked the door behind me. There, kid, now you're a little bit better protected. But will it do any good when you hear the Call?

'Move up,' said Olga. 'You're losing strength very fast. This level of the Twilight is a strain even for an experienced magician. I think I'll move up a level too.'

It was a relief to step out of it. No, I'm not an operational agent who can stroll around all three levels of the Twilight just as he likes. But I don't normally need to do that kind of thing.

The world turned a little brighter. I glanced around. It was a cosy apartment, not too polluted by the products of the Twilight world. A few streaks of blue moss beside the door . . . nothing to worry about, they'd die, now that the main colony had been exterminated. I heard sounds too, from the direction of the kitchen. I glanced in.

The boy was standing by the table, eating garlic and washing it down with hot tea.

'Light and Dark,' I whispered.

He looked even younger and more helpless than the day before. Thin and awkward, but you couldn't call him weak, he obviously played sport. He was wearing faded jeans and a blue sweatshirt.

'The poor soul,' I said.

'Very touching,' Olga agreed. 'It was a clever move of the vampires to spread that rumour about the magical properties of garlic. They say it was Bram Stoker himself who thought it up . . .'

The boy spat into his hand and started rubbing garlic on to his neck.

'Garlic's good for you,' I said.

'Oh yes. It protects you. Against flu viruses,' Olga added. 'How easily the truth is lost, and how persistent lies are . . . But the boy really is strong. The Night Watch could do with another agent.'

'But is he ours?'

'He's not anyone's yet. His destiny's still not been determined, you can see for yourself.'

'But which way does he lean?'

'There's no way to tell, not yet. He's too frightened. Right now he'd do absolutely anything to escape from the vampires. He's equally ready to turn to the Dark or the Light.'

'I can't blame him for that.'

'No, of course. Come on.'

The owl fluttered into the air and flew along the corridor. I walked after her. We were moving three times faster than humans now: one of the fundamental features of the Twilight is the way it affects the passage of time.

'We'll wait here,' Olga announced, when we were in the lounge. 'It's warm, light and comfortable.'

I sat in a soft armchair beside a low table and glanced at the newspaper lying there.

There's nothing more amusing than reading the press through the Twilight.

'Profits on loans down', said the headline.

In the real world the phrase was different: 'Tension mounts in the Caucasus'.

I could pick up the newspaper now and read the truth. The real truth. What the journalist was thinking when he wrote on the topic he'd been assigned. Those crumbs of information that he'd received from unofficial sources. The truth about life and the truth about death.

Only what for?

I'd stopped giving a damn about the human world a long time ago. It's our basis. Our cradle. But we are Others. We walk through closed doors and we maintain the balance of Good and Evil. There are pitifully few of us, and we can't reproduce – it doesn't follow that a magician's daughter automatically becomes an enchantress, and a werewolf's son won't necessarily be able to change his form on moonlit nights.

We're not obliged to like the ordinary, everyday world.

We only guard it because we're its parasites.

I hate parasites!

'What are you thinking about now?' asked Olga. The boy appeared in the lounge. He raced across into the bedroom – very quickly, bearing in mind that he was in the everyday world. He started rummaging in the wardrobe.

'Nothing much. Just feeling sad.'

'It happens. During the first few years it happens to everyone.' Olga's voice sounded completely human now. 'Then you get used to it.'

'That's what I'm feeling sad about.'

'You should be glad we're still alive. At the beginning of the twentieth century the population of Others fell to a critical threshold. Did you know there were debates about uniting the Dark Ones and the Light Ones? That programmes of eugenics were developed?'

'Yes, I know.'

'Science came close to killing us off. They didn't believe in us, they wouldn't believe. That is, while they still believed science could change the world for the better.'

The boy came back into the lounge. He sat down on the sofa and started adjusting the silver chain round his neck.

'What is better?' I asked. 'We were people once, but we've learned to enter the Twilight, we've learned to change the nature of things and other people. And what's changed, Olga?'

'At least vampires don't hunt without a licence.'

'Tell that to the person whose blood they drink.'

The cat appeared in the doorway and fixed his gaze on us. He howled, glaring angrily at the owl.

'It's you he doesn't like, Olga,' I said. 'Move deeper into the Twilight.'

'Too late,' Olga replied. 'Sorry, I let my guard down.'

The boy sprang up off the sofa. Far faster than is possible in the human world. Clumsily, without even knowing what was happening to him, he entered his shadow and immediately fell on the floor, looking up at me. Through the Twilight.

'I'm leaving . . .' the owl whispered as she disappeared. Her claws dug painfully into my shoulder.

'No!' shouted the boy. 'I know! I know you're here!'

I started to get up, spreading my hands.

'I can see you! Don't touch me!'

He was in the Twilight. He'd done it, just like that. Without any help from anyone, without any courses or stimulants, without any magician to tutor him, the boy had crossed the boundary between the ordinary and the Twilight worlds.

The way you first enter the Twilight, what you see and what you feel there goes a long way to determine who you'll become.

A Dark One or a Light One.

' We have no right to let him go over to the Dark Side, the balance of power in Moscow would completely collapse.' The boss's words came back to me.

Okay, kid, you're right on the edge.

That was more terrifying than any inexperienced vampire.

Boris Ignatievich was entitled to have the boy taken out.

'Don't be afraid,' I said, not moving from the spot. 'I'm your friend and I won't do you any harm.'

The boy crawled as far as the corner and froze there, never once taking his eyes off me. He clearly didn't understand that he'd shifted into the Twilight. It looked to him as if the room had suddenly turned dark, a silence had fallen and I'd appeared out of nowhere . . .

'Don't be afraid,' I repeated. 'My name's Anton. What's your name?'

He didn't say anything. He kept gulping, over and over again. Then he pressed his hand against his neck, felt for the chain and seemed to calm down a bit.

'I'm not a vampire,' I said.

'Who are you?' the boy yelled. It was a good thing that piercing shriek couldn't be heard in the everyday world.

'Anton. A Night Watch agent.'

His eyes opened wide, as if he were in pain.

'It's my job to protect people against vampires and all sorts of vermin.'

'You're lying . . .'

'Why?'

He shrugged. Good. He was trying to assess his actions so far and explain his reasons. That meant the fear hadn't completely paralysed his mind.

'What's your name?' I asked again. I could have influenced the boy and removed his fear. But that would have been an intervention, and a forbidden one.

'Egor.'

'A good name. My name's Anton. Do you understand? I'm Anton Sergeevich Gorodetsky. A Night Watch agent. Yesterday I killed a vampire who was attacking you.'

'Just one?'

Excellent. Now we had the makings of a conversation.

'Yes. The girl got away. We're searching for her now. Don't be afraid, I'm here to guard you ... to destroy the vampire.'

'Why is everything so grey?' Egor suddenly asked.

Good boy. That's really good going.

'I'll explain. Only first let's agree that I'm not your enemy. All right?'

'We'll see.'

He held on to his absurd little chain, as if it could save him from anything. Oh, kid, if only everything in this world was that easy. Silver won't save you, or poplar wood, or crucifixes. It's life against death, love against hate . . . and power against power, because power has no moral categories. That's how simple it is. In the last couple of years I've come to realise that.

'Egor,' I said, walking slowly across to him. 'Listen, I want to tell you something.'

'Stop!'

He shouted the command as sharply as if he were holding a weapon in his hands. I sighed and stopped.

'All right. Now listen. Apart from the ordinary world that the human eye can see, there is also a shadow world, the Twilight world.'

He thought. Despite his fear – and he was terribly afraid, I could feel the waves of his suffocating horror washing over me – the boy was trying to understand. There are some people who are paralysed by fear. And there are some whom it only makes stronger.