The gym is situated at the back of the school. There are several buildings behind it, shops and a factory. No direct way through, except for a narrow alley included at the insistence of the local authorities.

Trev's ducking through a small door when I catch up. The others have gone ahead. He looks back as I rush after him, afraid I'm a zombie. He smiles fleetingly when he recognizes me, then stands aside and lets me pass.

"This way!" he yells, waving his arms over his head.

"What are you doing?" I snap.

"We've got to help the rest of them," he pants.

I study the scores of students fighting with those who've been turned into zombies. Lots are trying to escape through the main doors. Some are trying to climb the walls, to get to the skylight windows that lead to the roof, but they've no hope - too smooth, too high, no ladders or ropes. Others have collapsed mentally and huddle on the floor, weeping, praying, shaking their heads, hoping the zombies will leave them alone or that they'll wake up and find out this was just a dream.

"Forget about them," I tell Trev.

"But we can't just - "

"If you keep on shouting, you'll alert the zombies. You want them coming after us?" He stares at me, tears in his eyes. "Best thing we can do is get out and call for help, Trev. It's their only hope."

Trev looks around the gym, then curses and shoves through after me.

We're in a small corridor, me, Trev, Ballydefeck, Suze, La Lips, Elephant, Meths, Linzer, Copper, Stagger Lee, Pox, Dunglop. Tyler's with us too, and a few others, two black guys, an Indian, three Muslims, a white kid called Rick.

"Where's Kray?" Trev asks.

"One of them got him," Suze sobs. "It cracked his head open. I saw it... his brains... it..."

"What the hell's going on?" the tallest of the black kids roars. "How'd they get in? Where'd they come from? I thought they only came out at night."

We stare at him in silence. Then I shrug. "We'll ask questions later. Let's get out of here before the brain-munching bastards find us."

We hurry down the corridor. The emergency exit's at the end. It opens out into the alley that runs between the two buildings behind the school. I've been through it a few times during fire drills. Never thought I'd have to do this for real, or that I'd be running from zombies, not a fire.

Ballydefeck gets to the door first. He slams down on the access bar and pushes.

Nothing happens.

"Out of the way," the tall black guy snaps. He bangs the bar down and shoves hard.

Nothing happens.

"Everyone," I shout. "Push together."

We crowd around the door. I get some fingers on the bar. It slides down smoothly when we push but the door doesn't give, not even a crack.

"Forget the bar," Trev says. "Focus on the door."

We strain, silent, red-faced, sweating, shoving with everything we have.

The door doesn't move.

"It's jammed shut," Ballydefeck says.

"Can we cut through?" Tyler asks.

"With what?" Pox yells. He got his nickname because of the spattering of facial scars left behind when he had the chicken pox. The scars aren't normally very prominent, but now that his face is scrunched up with terror, he looks like a rabid monkey. I almost make a joke out of it, but this isn't the time to be a wiseass.

"We're all gonna die," La Lips wails.

"Shut up," I tell her. "Trev?" I look to him, hoping he'll have an answer.

"There's another exit to the alley on this side of the building, on the floor above," he says. "Or there's the front door."

"Which do you think we should - "

A scream stops me. My head whips around. A small girl is dangling from Pox's right arm, teeth locked on his flesh, chewing her way down to the bone.

Pox screams again and slams the girl into the wall. She doesn't let go. He jabs at her face with the fingers of his free hand. In a swift movement she releases him and snaps at his fingers. Catches them and grinds down. Pox screams louder and falls to his knees.

I start towards them but the black kid who beat me to the bar beats me to the girl too. There's a flick knife in his right hand. He slashes the blade across the girl's chest. She loses interest in Pox and pushes her attacker away. Looks at the gash in her chest. Gurgles, then throws herself at the teenager with the knife.

He keeps his cool. Ducks the girl's attack, then jabs the knife at her face. She winces when it strikes. He winces too. I can see horror in his eyes. He's never done anything like this before. But when the zombie snaps at his fingers, he thrusts the horror away, grits his teeth and digs the knife deeper into her head. She swipes at him, squealing and snapping at his fingers.

"Hold her down!" he roars.

Trev and I react quickest and wrestle her to the floor. She snaps at the black kid again but he keeps his fingers clear of her mouth. Drives the knife deep into her head, panting like a dog. Again. Blood flows. Bone splinters. He doesn't stop. Moments later he's gouging out chunks of brain, making sobbing noises. The girl shudders, moans, spasms. He keeps it up, face grim, silent now, teeth bared. Finally she stops moving and her eyes go steady in their sockets.

"Is she dead?" Trev asks.

"Yeah," he croaks, getting up, wiping tears from his cheeks. He's trembling wildly, his left hand shaking like mad. But his right hand - his knife hand - is steady as the blade itself.

"How can we be sure?" Stagger Lee asks.

"I destroyed her brain," the black kid grunts.

"That works in movies, but we don't know for sure that it happens that way in real life," I note, eyeing the dead girl nervously. "What if she comes back to life and attacks again?"

He laughs edgily. "Then we're screwed."

I look up, shocked, then laugh with him. It's that or go mad.

"How'd you sneak in the knife?" I ask.

"I never leave home without it. Been mugged too many times."

"If the teachers found it..."

"That lot don't know how to find their own arseholes."

My smile spreads. "I'm B," I tell him.

"Cass."

"Isn't that a girl's name?"

"Short for Cassius. After Muhammad Ali's real name."

"Sweet." I show my knuckles and let him knock them.

"We killed her," Suze cries.

"We had to," Cass says, then takes a deep, steadying breath. "We've gotta get out of here."

"But - " Suze says.

"Shut it," Meths snarls. He's still holding the ball, which he must have picked up when the game stopped.

"Are you all right?" I ask Pox.

He's bleeding, shaking like an old geezer with Parkinson's, even worse than Cass was, but he nods. "I'll live," he moans, taking off his sweatshirt and using it to wipe blood from his arm and fingers.

"But as what?" Cass says, blade still extended, pointing now at Pox.

"What do you mean?" Pox frowns.

"We've all seen zombie films. You've been bitten. If you turn into one of them..."

"I won't!" Pox squeaks. As Cass glares at him, Pox looks for support. "B? You're not gonna let him do me, are you?"

I glance at the others but nobody meets my eye, happy to leave the decision to me now that it's been placed in my hands. Bloody cowards.

"B?" Pox wheezes, real terror in his eyes, fresh tears trickling down his cheeks and gathering in the pockmarks in his flesh. "Are you gonna...?"

"No," I mutter. "But keep behind the rest of us, all right? And if we think you're starting to change, we'll have to cut you loose."

"But - "

"No time to argue, Pox. Accept the rules or it's the knife." I turn to Cass. "What do you reckon - make a break for one of the exits, or find a place to hole up and wait for help to arrive?"

"Nobody helped those buggers in Pallaskenry," Copper says. "The only ones who made it out alive were those who got out early. The soldiers surrounded the place once they hit the scene and shot anyone who moved, normal people along with the zombies."

"Run?" Cass asks.

"Run," I agree.

And we're off.