I want it to be a joke, some smartarses screwing with the rest of us. I'd be so happy if they were winding us up, I wouldn't care that I'd been made a fool of. I'd laugh, admit I fell for it, hail them as champion pranksters.

But the blood's real. The terror. The screams.

And the zombies.

I spot the first of them coming. A boy I don't recognize. His sweater and shirt are ripped. His stomach has been carved open. Guts ooze from holes as he lurches forward. His eyes are unfocused, his lips caked with blood. He moves stiffly but purposefully.

The undead boy grabs the girl who screamed. Pulls her hair back. Sinks his teeth into her throat. Rips out a strip of flesh and gurgles happily as blood sprays his face.

I've seen blood fly in fights, movies and computer games. But never like this. Nothing I've ever seen before has prepared me for this.

The spell breaks and pandemonium erupts. Everyone's screaming at once. People run in circles, crash into one another, fall, thrash around on the ground, lash out with their feet and fists.

More zombies stream into the gym, boys, girls, a couple of teachers. They zone in on the living, hunting like wolves. They have a sweet time of it. In all the mayhem, lots of kids try to rush by them. Easy prey. The zombies just reach out and snatch.

I haven't moved. I'm watching sickly, numbly studying the undead as they feast on their victims. Some of the kids writhe and curse as they're bitten, moan and weep and beg for mercy. The zombies don't care. They tear with their fingers and teeth, bite, claw, rip, chew.

"Stop that!" Stuttering Stan roars. He strides forward, blowing his whistle, trying to wave back the zombies. The fool thinks that he can control this, the same way he can control violence on the pitch.

A zombie boy my age butts Stuttering Stan in the chest. As the teacher falls back, winded, the boy sticks his fingers into the adult's left eye and pokes it out. As Stuttering Stan screams, the boy gobbles the eye. Then he falls on his victim and digs through the hole where the eye should be, burrowing through to Stuttering Stan's brain.

"Come on!" Trev shouts, grabbing my arm. "We have to get out of here!"

"What?" I blink.

"They're gonna kill us, B!"

I look at the zombies and shake my head. "Not all of us. There's a pattern."

"What the hell are you talking about?" he barks.

I point. The zombies aren't killing everyone. As each one enters the gym, he or she cuts or bites a few people, leaving them to yell and flee. Only then does the zombie settle on a target, break their skull and dig into their brain. Once they start to feast, they sit there, gorging, ignorant of everything going on around them.

"There's a pattern," I mutter again.

Before I can make sense of it, Trev shouts, "We're going. You can stay and let them eat you if you want."

I glance at him and the others in our gang. They're racing towards the rear left corner of the gym. My senses click - there's an emergency exit there.

I stare at the carnage, the kids going wild, the zombies tucking in. I was in a daze before this, detached and calm. But now that I focus, I realize I'm dead if I don't move quickly.

"Sod this!" I moan, then tear after the others as fast as I can.