It's late and out here the world is silent. The noise of battle has long since faded away to nothing. Still surrounded by hordes of others we move quickly through the empty countryside. Armed scouts guide us through the darkness. I don't know where we're going, but I know that I can trust these people and I follow on regardless. I have a feeling in the pit of my stomach which tells me that before long I might finally start getting answers to some of the thousands of questions I've been desperate to ask.

We've marched for more than an hour now and have seen and heard no-one else. Our route has avoided all roads and buildings and virtually all other signs of civilisation. Now we're moving along the base of a deep valley, shielded from view by trees and bushes.

We stop.

'In here,' one of our guides says, ushering us towards a large copse. Without question we move into the trees, stopping only when we've reached the densest part of the woods. The light in here is almost non-existent. One of the scouts kicks around in the undergrowth, seeming to be looking for something. Her foot strikes a small mound in the leaf-covered ground. She bends down and grabs the strap of a bag which one of them must have hidden there previously. She pulls the strap and drags up a large rucksack. Leaves and dirt fall from it as she stands it up and brushes it down. She opens the pack and starts to empty it out.

'Sit down and rest,' one of the other scouts says as his colleague throws packets of food and bottles of water to us. 'Get your strength back,' he continues, 'then listen to the message and leave.'

The message? What message? What's he talking about? I decide that I'll find out later. Right now eating my first food in more than a day is more important than anything else.

I'm sitting with three other people. In the middle of us is a mobile phone, set up ready to play the message. This message, our guides inform us, is as close to the truth as we'll get tonight. It has been distributed as a file by people like us and has spread around the country like a computer virus. It now sits on hundreds of thousands of phones, computers, media players and other devices, too widespread to be deleted.

'Chris who?' a man sitting next to me asks.

'Chris Ankin,' one of the guides replies.

'Who the hell's he?'

'He was a politician,' he explains. 'Used to be fairly high-ranking in Defence. He was an adviser to the government when it began. He got to hear a hell of a lot of information before he changed.'

'So where is he now?'

'Rumour has it he's dead.'

'Great.'

'Doesn't matter. He did what he wanted to do before they got him.'

'What was that?'

'He wanted to let us know what was happening. He wanted to warn us. He wanted to try and coordinate us.'

'Coordinate us?'

'Make sure we all know what we have to do.'

'And what's that?'

'Why don't you just play the fucking message?'

The man leans forward and picks up the phone. He struggles with the controls for a second but soon manages to locate the file and starts it playing. At first the words are hard to make out. He adjusts the volume and lifts up the phone so that we can all hear what's being said.

'If you're listening to this,' Ankin's weary voice says, sounding tinny and distorted, 'chances are you don't have a clue what's happened to you or what's happened to the rest of the country. You won't know why you feel the way you do or why your life has just been turned upside down. I'll give you some information but I won't be able to answer all of your questions. I'll tell you what I know but that's not what's important now. Ultimately it doesn't matter why this has happened or what caused it, what matters is how we deal with it. Because of the unprecedented nature of the change and its effects on our society we need to act now and we need to act quickly. There will be time enough to look for reasons when the fight is over.'

I shuffle on the ground and glance at the other faces gathered around the telephone. They stare at the small handset with bewildered expressions. I'm not sure if anyone believes what they're hearing.

'Put simply,' Ankin's voice continues, 'there is a fundamental genetic difference between us and them. A fundamental and basic difference which, until now, has remained dormant. I can't yet tell you why, but something has happened to trigger a change, and that change has created the hate. If you're hoping for me to give you a more scientific explanation, I can't. If you're waiting for me to explain why we can no longer exist alongside the people we loved, lived with and worked with just a couple of weeks ago, I can't. One day we'll understand, but today we don't have the luxury of having either the time or resources to find out.

'Initially it was presumed that the change was limited to just a small minority of people. Before it happened to me, while I was still in office, I saw figures which indicated that our numbers are much greater than was first thought. It's likely that as many as three people in every ten are like us. That's around thirty percent of the population. That's enough to take the fight to them and stand a chance.

'The change strips away some of the restraint we used to have. In very basic terms it makes us less susceptible to bullshit and more likely to take action. The change seems almost to amplify our instincts. We immediately know who is like us and we know who isn't. We know who poses a threat to us and who is on our side. Many of the layers of conditioning and control imposed upon us by society have been stripped away by the change and no longer apply. Now you fight when you need to fight and you destroy the enemy because you know that they will destroy you if you give them half a chance.

'Until now we've discriminated against each other according to race, religion, age, gender and just about every other differentiation imaginable. Look around you tonight and you'll see that those differences are gone. Now, to put things as simplistically as possible, there is just 'us' and 'them', and it is impossible for us to coexist. We have no alternative but to fight, and we must keep fighting until we have wiped them out.

'The change has spread across the world with an incredible speed. No corner of the planet has been left untouched. We are everywhere. You must remember that we are not the underdogs. Their advantage over us is in physical numbers only. We have served at every level and among us we have experts in every profession. Among us we have every skill imaginable. We have everything we need to fight them and destroy them.

'Forget your past. Forget your families and friends and who you used to be. In time some kind of normality will be restored. Until then we have no alternative but to fight.'

The message ends and I look at the phone in disbelief. Is this a joke? Can any of this really be true? For a moment I'm overloaded, unable to take it all in. Then my mind begins to fill with memories of the events of the last week and particularly of the last day - the killings, the battles, the bloodshed, the emotions - and I know that every word I've just heard is true. I remember the feelings of strength and power I felt as I killed the enemy soldiers with my hands just a few hours ago and I know that it's all real. Impossible and unproven but real.