The room was made even more cramped by a stack of cardboard boxes at the far end. They'd once contained all their food and bottled water, but there was virtually nothing left now. They had supplies for two more days, maybe three if they were careful. Jack was looking through the pile, chucking empty boxes aside.

There came an even bigger bang and the wardrobe appeared to shake slightly. They'd packed it with junk to make it heavier and it would need a pretty hefty shove from outside to knock it out of the way, but it wasn't impossible.

'We've got to get out of here,' Jack muttered.

'What?' Ed frowned at him.

'I said we've got to get out of here.' This time Jack's voice came through loud and clear and everyone listened. 'It's pointless staying. Completely pointless. Even if that lot out there back off in the morning, even if they crawl back to wherever it is they're sleeping which we don't know for certain they will do we're gonna have to spend all day tomorrow going round trying to block up the doors and windows again. And then what? They'll only come back tomorrow night and get back in. We can't sleep, we can't eat. Luckily none of us got hurt tonight, but ... I mean, if the teachers don't get us, we'll basically just starve to death if we stay here.'

'Yeah, I agree,' said Bam. 'I reckon we should bog off in the morning.' Bam's voice sounded very loud in the cramped dormitory. He had always had a tendency to shout rather than speak and before the disaster the other boys had found him quite irritating. He was large and loud and boisterous. Blundering around like a mini tornado, accidentally breaking things, making crap jokes, playing tricks on people, laughing too much. Now the others couldn't imagine how they'd cope without him. He never seemed to get tired or moody; he was never mean, never sarcastic, and totally without fear.

'We need to find somewhere that we can defend easier than this,' Bam went on. 'Somewhere near a source of food and water.'

'The only source of food around here is us,' said Jack.

'They might go away,' said Wiki's friend Arthur. 'They might all die in the night lots of them are already dead. If we hold on long enough, they'll all die, they'll pop like popcorn. You see when Miss Jessop, the science teacher, died? She was lying on the grass in the sun, lying down dead and her skin started to pop like popcorn, the boils on her kept bursting, like little flowers all over her. You see like when flowers come out in a speeded-up film? Pop, pop, pop, and after a while there wasn't anything left of her, she was just a black mess, and then a dog started to eat her and the dog died, too.' Arthur stopped and blinked. 'I think we should stay here until they all go away or pop like popcorn.'

'They're not going to go away,' said Jack, going over to the window where Chris was still reading his book, his eyes fixed on the pages. There was a bright moon tonight, and it threw a little light into the room, but Jack doubted if it was enough to see the words properly. Not that that stopped Chris. Nothing could stop him now.

Jack looked down into the street. There were two teachers down there and an older teenager, maybe seventeen or eighteen. They were hobbling along, walking as if every step hurt their feet.

'Some of them die from the disease and some don't,' he said. 'Who knows why?' He turned back from the window to point towards the door where one of their attackers was rattling the handle. 'And who knows how long that lot out there are going to take to die? Could be weeks, and in the meantime they know we're here and they won't give up until they've got us. They're going to keep on attacking, every night, soon as it's dark, every bloody night. Most of the other boys left ages ago. Us lot, we stayed in case anyone turned up to rescue us. Ha, good one. Nobody has turned up, and, let's face it, nobody will.'

'Two billion three hundred and sixty-five million and two hundred thousand seconds ...' said Wiki quietly. 'Roughly. In a lifetime. If you're lucky ...'

5.

It took four of them to shift the wardrobe aside in the morning. Aware that they were moving it for the last time.

Once the door was clear Bam put his ear to it. He looked at Jack. Jack licked his lips, tense.

'Well?'

Bam shook his head. 'Can't hear anything.'

'Go on then.'

Bam grasped the handle, turned. It clicked and the door popped open a fraction. He checked that everyone was ready. A row of boys stood waiting. They'd pulled the metal bed frames apart to make weapons out of the struts and heavy springs, and they'd packed up whatever supplies and belongings they had left into backpacks or bundles made out of sheets.

'Ready?'

The boys nodded. Bam took a deep breath and tugged the door open.

A pale, sickly light washing in from the small windows showed that the area outside was empty.

The teachers had gone.

One by one the boys filed out on to the landing, wary and alert. They were shivering. Their combined body heat had kept them reasonably warm in the dormitory, but it was early March and the air out here was noticeably colder.

'Look at that.' Johnno nodded towards the door. The outside of it looked like it had been savaged by a pack of wild animals. There were gouges and great dents, long gashes, as if from claws. It was worst round the handle. The teachers had almost managed to scrape right through the wood. The walls were similarly scarred, with chunks missing and a pattern of bloody handprints.

'Looks like we only just made it out in time,' said Bam. 'One more night and they'd have been on us.'

It stank on the landing. There was evidence that at least one of the teachers had used the carpet for a toilet. There was torn wallpaper down the stairs and a fresh splash of blood up one wall. Maybe they'd been fighting among themselves.

'Come on.' Bam led the way down. Behind him came Johnno and his other mates from the rugby team, carrying vicious metal lengths of bed frame, with ripped-up sheets wrapped tightly round the ends to protect their fingers. Next came Jack and Ed, Jack with the cricket bat, Ed with a hockey stick. Behind them were Arthur and Wiki, chatting away to each other, wobbling bedsprings up and down in their hands. Then Chris Marker, still reading a book as he walked, a makeshift pack slung over his back crammed with yet more books. Then the three nerds, carrying wooden clubs made from chair legs. After them came Kwanele, immaculate as ever in his suit and tie, lugging an expensive suitcase and suit bag, filled with his favourite outfits. Finally the six boys from Field House, watching their rear and armed with an odd assortment of garden tools.

At the bottom of the stairs the carpet was black and sticky, as if a tub of treacle had been poured into it. The boys' trainers stuck to the floor and squelched as they lifted their feet. It smelt worse down here, a foul brew of blood and dead flesh and unwashed bodies. Sweet and sour and putrid.

The main way in and out of the building was through two big double doors. The first thing Mr Hewitt had organized when they'd decided to secure the House was nailing the doors shut with planks of wood. They'd been using an alternative exit through the back of the kitchen as a way in and out, because it was quicker to open and close and easier to lock. They had keys for the back door as well as the kitchen door, so had an extra line of defence. It had turned out to be a complete waste of time, though, as the sick teachers soon found other ways to get into the House.

Bam put a hand over his mouth to block the stink.

'This way,' he said, leading the group down the corridor that led towards the kitchen.

It was dark in the corridor and they walked quickly. All the boys wanted to get outside as fast as possible. They soon arrived at the kitchen door, which had a small, reinforced-glass window set in the centre, crisscrossed with a wire mesh.

Bam strode up to it, as eager as the others to be out of here. He took a big bunch of keys from his pocket, selected the right one and slotted it into the lock. He was just about to turn it when Jack pulled him back.

'Wait a minute.'

Bam stopped. A flash of irritation. Then a little laugh.

Jack sighed. 'Come on, Bam, you could at least check it before you open it.'

'Sorry, old mate, brain not in gear. Never did work at a hundred per cent, to tell you the truth, turned to mush now. Still asleep, I think.' He knocked the side of his head with his fist. 'Wakey, wakey!'

Jack stuck his nose to the little window and peered into the kitchen. It was dark; the sun rose on the other side of the building and its light hadn't reached this far yet. He could see no movement in the gloom. Then he spotted that the back door was half open. Someone had definitely been in there during the night.

'What do you reckon?' Bam asked. 'Is it safe?'

'Hang on a minute. Can't tell.'

Jack's eyes were slowly growing used to the light. He was picking out more details in the kitchen. There was a scarlet smear of blood on the window over the sinks. And there, on the table, what looked like a slab of meat. He realized there was an arm still attached to it. He swallowed, trying not to retch.

'I'm not sure we should go this way,' he said.

'Are there some of them in there?' Bam asked, trying to see over Jack's shoulder.

'It's hard to tell.'

'Here, let me look.' Bam shoved Jack aside and took his place at the window.

'Not a pretty sight, is it? Don't think there's anyone in there, though ... Whoa!' He leapt back as a female teacher hurled herself at the door, squashing her face against the glass and smearing it with pus. It looked like Miss Warlock, from the English department, but it was hard to tell.

The shock made Bam burst out laughing and soon most of the other boys had joined in. Jack just stared at the door, which shook on its hinges as Miss Warlock repeatedly rammed herself against it with a whining and a slobbering noise.

Ed crept forward and risked looking in.

'There's more than one of them in there,' he said. 'We'll have to go another way.'

'You don't say,' Jack murmured.

'And we need to be quick,' said Ed, ignoring Jack. 'They could break this door down if there's enough of them. Or they might just figure out that there's another way in however they all got in last night.'

They backtracked down the corridor, increasingly nervous and anxious to be out of the building that was feeling more and more like a trap. When they got back to the hallway, they headed for the doors.

Jack saw what looked like a football sitting in the middle of the floor. He had an urge to race forward and kick it, an automatic response. He took several paces then came to a dead stop, almost overbalancing, like someone suddenly finding themselves at the edge of a cliff in a cartoon film.

It wasn't a football. It was a human head. All that was left of Mr Hewitt. His eyes were open, and he looked calm and at peace. He no longer resembled the deranged maniac he'd been when Jack last saw him.

Now Bam spotted the head.

'Bloody hell,' he said with a laugh. 'Better get rid of that. Bit freaky.'

He picked the head up gingerly by the hair then lobbed it across the room towards a waste bin that sat in a dark corner. Amazingly it landed cleanly inside. Bam cheered and punched the air.

'Shot!'

Jack didn't know whether to laugh or curl up in a ball and bang his forehead on the floor in despair. He stood there, drained of all energy, wishing he was a million miles away.

Bam, Johnno and Piers, with bits of iron bedstead, set to work on the door, trying to lever the planks off. It was slow work, made slower by the fact that the boys had hardly slept again in the night and were strung out, awkward and sluggish, their muscles not working as they should, as if the signals weren't getting through clearly from their brains. In the end Jack couldn't bear to watch them clumsily struggling to make any headway; he came back to life and went over to help.

As they worked, they could hear the teachers down the corridor, bashing and thumping against the kitchen door.

'Can't you hurry up?' said Kwanele, who was standing back, watching, his luggage sitting neatly at his feet, for all the world as if he was waiting for a train.

'We're going as fast as we can,' said Bam.

'If you're in so much of a hurry,' said Jack irritably, 'why don't you help? Or don't you want to get your clothes messed up?'

'I'm not very good with my hands,' said Kwanele, flattening a lapel on his suit jacket. 'And, yes, I don't want to ruin my clothes. This shirt is Comme des Garcons.'

Jack shook his head and tutted. If Kwanele wasn't so ridiculous, the others would have long ago lost patience with him.

There was one last plank left to remove. Bigger and thicker than the others, with about ten fat nails fixing it to the door. The boys were getting in each other's way and Johnno's weapon slipped, gouging Piers' hand. Piers sucked his fingers and swore at him.

There came an almighty crash from the kitchen.

Jack glanced back. Had the door finally given out?

'Come on, come on,' he said, as much to the piece of wood as to the other boys. He was scrabbling at the plank with his fingers, trying to prise it loose, and he was so intent on removing it that he lost track of what was going on behind him. It was only when he heard a high-pitched scream that he turned round.

There were teachers in the hallway. Six of them, including Monsieur Morel, who had his hands at the throat of one of the Field House boys and was shaking him like a doll. The boy's friends were battering the teacher with their makeshift weapons. The rest of them were being kept back by the Sullivan brothers and the three nerds, who stayed in a tight pack, yelling and screaming abuse.

Ed was with the rest of the boys, who were milling in a frightened circle, not sure what to do.

Johnno gave his iron strut to Jack and snatched a fire extinguisher from a bracket on the wall.

'You get the door open,' he shouted. 'We'll deal with this lot.'

Ed ran over to help Jack and between them they managed to get the bit of bedstead behind the plank. They pulled down on it with all their weight and with a horrible squealing noise the nails began to pull loose.

Johnno hit the plunger on the top of the extinguisher and a stream of white foam erupted from the hose. He aimed it at the circling teachers, blinding them.

Monsieur Morel was still savaging the boy from Field House. The blows raining down on his back seemed to be having no effect.

With a final screech, the plank popped off the door. Jack grabbed one end and raced back to Morel.

'Out of the way!'

He swung the piece of wood at the man's head and it stuck fast. One of the nails must have punched through his skull. Morel stood up, the plank hanging from the back of his head like a huge ponytail. He stretched out an arm towards Jack, then went stiff and shuddered before falling sideways, knocking over Miss Warlock, who slipped and slithered about on the floor, unable to stand up in a pool of melting foam.

'Come on,' Bam yelled from the doorway. 'Let's go! Let's go!'

'We don't know what's out there.' Ed looked worried.

'Can't be any worse than what's in here,' Jack shouted as he ran over and pushed past Ed.

Ed closed his eyes and took a deep breath, trying to find some small scrap of courage hidden deep inside.

When he opened his eyes, he realized that he'd been left behind. The others had already gone outside. He hurried after them and found them in a tight pack, blinking in the early-morning light. The boys from Field House looked shell-shocked. Ed realized their friend hadn't made it. He said nothing. Too sick to speak.

There didn't appear to be anyone else around out here, but a low moan from behind him caused Ed to turn around. The teachers were emerging from the House, covered in foam. They were too sick to move fast, and the boils and sores covering their skin made them walk as if they were treading barefoot on broken glass, but the boys knew from experience that they wouldn't stop. Once they started to follow they wouldn't give up.

'Leg it!' Bam shouted, and the boys raced across the open ground towards the main school entrance.

Ed stayed at the back, helping Wiki and Arthur. They were smaller than everyone else and slower. Ed didn't know what he'd do if one of them got left behind. He urged them on, shouting encouragement, aware all the time that the teachers were steadily lumbering along behind them.

They rounded the end of School House and headed towards the archway that led out into School Yard. Ed spotted Jack ahead. He was hanging back, staring at the administrative building by the main gates.

What now?

Ed was too scared to stop. He sprinted through the arch, but, as he ran past, Jack grabbed hold of his jacket and pulled him back.

Wiki and Arthur ran on.

'What's the matter?' Ed's voice rasped in his throat.

'Can you see that?' said Jack, and he blinked, as if not wanting to trust his own eyes.