At the radial line station the feeling of the target became almost unbearably strong. I'd already picked out a few likely prospects: two girls, a young guy, a boy. They were all potential targets, but which one of them was it?

My four candidates got into the same carriage. That was a stroke of luck at last. I followed them in and waited.

One girl got out at Rizhskaya station.

The feeling of the target didn't get any weaker.

The young guy got out at Alekseevskaya.

Great. Was it the girl or the boy?

I risked a stealthy glance at both. The girl was plump and pink-cheeked, she was absorbed in reading her MK newspaper, showing no signs of any kind of agitation. The boy, in contrast, was skinny and frail, standing by the door and tracing his finger across the glass.

In my opinion the girl was a lot more . . . tempting. Two to one it was her.

But then, in judgements like that the question of sex decides pretty much everything.

I'd already begun hearing the Call. Still not verbalised yet, just a slow, gentle melody. I immediately stopped hearing the sound from my earphones. The Call easily drowned out any other music.

Neither the girl nor the boy showed any signs of alarm. The target either had a very high threshold of resistance or had simply succumbed straight away.

The train stopped at Exhibition. The boy took his hand away from the glass, stepped out on to the platform and marched off rapidly towards the old exit. The girl stayed on the train.

Damn!

They were both still too close to me, I couldn't tell which one I was sensing.

And then the music of the Call soared triumphantly and words began to insinuate themselves into it.

A female voice!

I jumped out between the closing doors, and hurried after the boy.

The hunt was nearing its end at last.

But how was I going to handle things with no charge on my amulet? I didn't have a clue.

Only a few people had left the train and there were five of us on the up escalator. The boy at the front, a woman with a small child behind him, then me, followed by an ageing, seedy-looking army colonel. The colonel's aura was beautiful, a glittering mass of steel grey and light blue tones. I thought with weary humour that I could call on him to help. Even these days people like that still believe in the idea of 'officer's honour'.

Except that any help I could get from the colonel would be about as much use as a fly-swat on an elephant hunt.

I dropped the stupid idea and took another look at the boy. With my eyes closed, observing his aura.

The result was disheartening.

He was surrounded by a shimmering, semi-transparent glow. Sometimes it was tinged with red, sometimes it was flooded with a dense green and sometimes it flared up in dark blue tones.

This was a rare case. A destiny still undefined. Undifferentiated potential. This boy could grow up to be a great villain, he could become a good and just person, or he could turn out to be a nobody, an empty space, which is actually what most people are anyway. It was all still ahead of him, as they say. Auras like that are normal for children up to the age of two or three, but they disappear almost completely as people get older.

Now I could see why he was the one the Call was addressed to. There was no denying it – he was a real delicacy.

I felt my mouth starting to fill up again with saliva.

This had all been going on for too long, far too long ... I looked at the boy, at the thin neck beneath his scarf, and I cursed my boss and the traditions, the rituals – everything that went to make up my job. My gums itched, my throat was parched.

Blood has a bitter, salty taste, but this thirst can't be quenched by anything else.

The boy hopped off the escalator, ran across the lobby and out through the glass doors. Just for a moment I felt relieved. I slowed down as I followed him out, and just caught a sense of movement out of the corner of my eye as he ducked down into an underpass. He was already running, physically drawn by the lure of the Call.

Faster!

I ran over to a kiosk and said, trying not to show my teeth:

'The stuff that's six roubles, with the ring pull.'

The young guy with a pimply face handed me the quarter-litre bottle with a slow, sluggish movement – as though he'd been taking a drop himself to keep warm on the job. He warned me candidly:

'It's not great vodka. Not gut-rot, of course, it's Dorokhov, but, you know . . .'

'Got to look after my health, anyway,' I joked. The vodka was obviously fake, but right now that was okay by me. With one hand I tore off the cap with the ring pull and with the other I took out my phone and switched it to repeat dial. The young salesman stared – he must have been shocked that someone who could afford a mobile phone would buy such bad vodka. I took a swallow as I walked along – the vodka stank like kerosene and tasted even worse, it was definitely moonshine, bottled in the back of someone's garage – and ran to the underpass.

'Hello.'

Larissa wasn't there any more. Pavel's usually on night duty.

'This is Anton. It's somewhere near the Cosmos hotel, in the back alleys. I'm in pursuit.'

'You want the team?' The voice was beginning to sound interested.

'Yes. I've already discharged the amulet.'

'What happened?'

A street bum bedded down halfway along the underpass reached out a hand as if he was hoping I'd give him the bottle I'd just started. I ran on past him.

'Something else came up . . . Make it quick, Pavel.'

The guys are already on their way.'

I suddenly felt as if a red-hot wire had been stuck through my jaws. Hell and damnation . . .

'Pasha, I can't answer for myself I said quickly and rang off. I pulled up short, facing a police patrol.

Isn't that always the way? Why do the human guardians of law and order always turn up at the most inappropriate moments?

'Sergeant Kampinsky,' a young policeman announced briskly. 'Your papers . . .'

I wondered what they were planning to pin on me. Being drunk in a public place? That was probably it.

I put my hand into my pocket and touched the amulet. Just barely warm. But this wouldn't take a lot.

'I'm not here,' I said.

The four eyes that had been probing me in anticipation of easy pickings went blank as the last spark of reason in them died.

'You're not here,' they echoed in chorus.

There was no time to program them. I blurted out the first thing that came into my head:

'Buy some vodka and take a break. Now. Quick march!'

The order clearly fell on fertile ground. The policemen linked arms like kids out looking for fun and dashed off along the underpass towards the kiosks. I felt vaguely uncomfortable, picturing the consequences of my instructions, but there was no time to put things right.

I hurtled out of the underpass, certain I was already too late. But oddly enough, the boy still hadn't got very far. He was just standing there, swaying slightly, less than a hundred metres away. That was serious resistance. The Call was so loud now, it seemed strange to me that the occasional passers-by walking down the street didn't start dancing, that the trolleybuses didn't swing off the main avenue, forcing their way down along the alley towards their sweet fate . . .

The boy glanced round. I thought he looked at me. Then he set off again, walking quickly.

That was it, he'd broken.

I followed him, frantically trying to decide what I was going to do. I ought to wait for the team – it would only take them ten minutes to get here, at most.

But that might not turn out so good – for the boy.

Pity's a dangerous thing. I gave way to it twice that day. The first time in the metro, when I spent the charge of the amulet in a useless attempt to displace the black vortex. And now the second time, when I set out after the boy.

Many years ago someone told me something that I flatly refused to accept. And I still don't accept it now, despite all the times I've seen it proved right.

'The common good and the individual good rarely coincide . . .

Sure, I know. It's true.

But some truths are probably worse than lies.

I started running towards the Call. What I heard was probably not what the boy did. For him the Call was an enchanting melody, sapping his will and his strength. For me it was just the opposite, an alarm call stirring my blood.

Stirring my blood . . .

The body I'd been treating so badly all week was rebelling. I was thirsty, but not for water – I could quite safely slake my thirst with the dirty city snow without doing myself any harm. And not for strong drink either – I had that bottle of lousy vodka with me and even that wouldn't do me any damage. What I wanted was blood.

Not pig's blood, or cow's blood, but real human blood. Curse this hunt . . .

'You have to go through this,' the boss had said. 'Five years in the analytical department's a bit too long, don't you think?' I don't know, maybe it is a bit too long, but I like it. And after all, the boss himself hasn't worked out in the field for more than a hundred years now. I ran past the bright shop windows with their displays of fake Gzhel ceramics and stage-set heaps of food. There were cars rushing past me along the avenue, a few pedestrians. That was all fake too, an illusion, just one facet of the world, the only one accessible to humans. I was glad I wasn't one of them.

Without breaking my rapid stride, I summoned the Twilight.

The world sighed as it opened up. It was as if airport searchlights had suddenly come on behind me, casting a long, thin, sharp shadow. The shadow swirled up, gaining volume, the shadow was drawing me into itself – into a dimension where there are no shadows. The shadow detached itself from the dirty tarmac, swirling and swaying like a column of heavy smoke. The shadow was running ahead of me . . .

Quickening my stride, I broke through the grey silhouette into the Twilight. The colours of the world dimmed and the cars on the avenue slowed, as if they were suddenly heavy.

I was getting close to my goal.

As I dodged into the alleyway, I thought I would just catch the final scene. The boy's motionless, ravaged body, drained dry, the vampires disappearing.

But I wasn't too late after all.

The boy was standing in front of a girl vampire who had already extended her fangs, slowly taking off his scarf. He was probably not afraid now – the Call completely numbs the conscious mind. More likely he was longing to feel the touch of those sharp, gleaming fangs.

There was a young male vampire standing beside them. I sensed immediately that he was the leader of the pair: he was the one who was initiating her, he was introducing her to the scent of blood. And the most sickening thing about it was that he had a Moscow registration tag. Bastard!

But then, that only improved my chances . . .

The vampires turned towards me in confusion, not understanding what was going on. The boy was in their Twilight, I shouldn't have been able to see him ... or them either.

Then the male vampire's face began to relax, he even smiled – a calm, friendly smile.

'Hi there ...'

He'd taken me for one of his own. And he could hardly be blamed for his mistake: I really was one of them now. Almost. The week of preparation had not been wasted: I had begun to sense them . . . but I'd almost gone over to the Dark Side myself.