Two dabs later. The orange light is still pulsing and changing size. Although I can call it closer like the other patches, I can't send it away more than twenty or twenty-five feet. It's started to bug me, like an insect which keeps buzzing in front of my face. An uneasiness chews away at me every time I catch sight of it. I know it's crazy, worrying about a light, but I can't help myself. I have a bad feeling about this.

It's a lovely sunny day. Our teacher, Logan Rile, decided not to waste the weather, so we're having lessons outside, in one of the fields around Paskinston. There are thirty-four of us, a variety of classes and ages, sitting in a semi-circle around Logan. He's telling us about tectonic plates. Logan's not the best teacher. He sometimes forgets he's talking to children and gets too technical. Very few of us understand everything he says. But he's interesting, and the bits that make sense are fascinating. It's also fun when you do understand him - it makes you feel clever.

Some of the younger children from the cr��che have come with us. Their normal minder has gone to the fair and her replacement's finding it hard to cope with so many little ones. She was delighted when Logan offered to take a few off her hands for the day.

Art's playing with the orange marbles beside me. I shouldn't let him have them, but he really likes them. Anyway, he hasn't put them in his mouth yet. I keep a close eye on him, checking every couple of minutes to make sure both marbles are in sight - not in his stomach.

"So these plates are moving all the time?" Bryan Colbert asks. Bryan's one of the eldest children, nearly seventeen.

"Yes," Logan says.

"Then why don't countries move?"

"They do," Logan says. "The continents are drifting all the time. It's very slow, but it's happening. One day Australia will collide with America or Africa - I can never remember which -  and the effects will be catastrophic. New mountains will be thrust upwards. There'll be tidal waves. Dust will clog the air. Billions of people and animals will die. It might be the end of all life on this planet."

"All life?" Dave English - a kid a year younger than me - asks.

"Yes."

"But I didn't think that could happen. Everybody... everything... can't just die. Won't God keep some of us alive?"

"No god can prevent the end of life on this planet," Logan says in his usual serious way. "Or the end of life in this universe. Everything has an end. That's the way life is. But maybe there'll be a new beginning when our world ends. New life, new creatures, new means of existence."

"That's scary," Dave mutters. "I don't want everything to die."

"Nor me," Logan smiles. "But our wants are irrelevant. This is the way things are. We can accept the truth and deal with it, or live in ignorance. Death is nothing to be afraid of. Once you think it through and get it into perspective, it's not so bad. In fact, many people - "

"Now!" a woman screams, cutting Logan off. All our heads turn at once, as if our necks were connected. I see Mrs. Egin lumbering up behind us, fingers twitching, frothing at the mouth. "Now it happens! Up the throat, past the gums, look out world, here it comes!"

The pink light which I saw her stroking a few days ago has grown much bigger and now seems to be touching her just behind her head. It's pulsing quickly. Other patches of light around it are pulsing too, and moving towards it, as though magnetically drawn to it.

"Mrs. Egin?" Logan says, rising, signalling for the rest of us to stay seated. "Are you all right?"

"They said I couldn't do it! Thought I wasn't strong enough to summon them!" She laughs her witch's laugh, then sings, "Wrong! Wrong! Wrong! Now! Now! Now!"

"Mrs. Egin, I think you should - "

"You will see me die!" she shouts and her eyes scan the group, fixing on me. "Find the thief! Who's the thief? Find him!"

Fear comes shooting back. I'm not as afraid as when I was alone with her, but I'm pretty petrified. The others are too. We huddle close together, shuffling into a tighter group for protection.

Logan steps forward. "Let me take you home, Mrs. Egin. We'll get you to bed, I'll call for a doctor, and you'll be right as rain in - "

Mrs. Egin roars a word I don't know. Her lips are moving fast now, in that strange language she was speaking before. Logan stops short and hesitates. That scares me even more - it's bad news when your teacher is as frightened as you are.

The pulsing patches of light are moving faster, drawn towards the pink light. They merge with it, then flow into Mrs. Egin. Now she's glowing from within, the lights beneath her flesh, spreading through her body.

I stumble to my feet. "The lights!" I gasp.

Logan looks back at me. "Calm down, Kernel."

"But the lights! Can't you see them?"

"What lights?"

"Inside her! She's swallowing the lights!"

Mrs. Egin cackles while Logan stares at me dumbly. I glance around. Everyone's looking at me oddly. They can't see the lights. There's nothing any of them can do to stop this happening.

I focus on Mrs. Egin. A bulging, pulsing bubble of light has formed behind and above her, patches melting together, colours mixing, flowing into her. Her eyes are bowls of light. I can't see her lips - multicoloured froth hides them. Her skin appears to be rippling.

"Mrs. Egin," Logan tries again, facing her. "You have to - "

The witch shrieks triumphantly. A piercing note of wickedness and victory. I cover my ears with my hands. Logan covers his too. My eyes scrunch shut, but I quickly force them open a crack. I see Mrs. Egin stagger backwards. She goes stiff, arms wide at her sides, head cocked to the left. A gentle, tender smile crosses her lips.

Then the lights explode through her. And she explodes. Scraps fly everywhere - flesh, bone, guts, blood. Logan and the kids at the front are splattered by the spray. They squeal with disgust and terror. A chunk of bone hits Logan hard in the face and he drops, grunting with pain.

I cover my eyes and drag Art in close, turning him away from the carnage. I'm screaming. Everybody is. But I can still hear Mrs. Egin's scream over the sound of all the others, even though she can't be making any noise now.

For an uncountable number of seconds the witch's scream holds, mingling with ours. Then it stops. All the screaming stops in the space of a second or two. Eerie, unnatural silence.

I don't want to take my arm away, but I must. I have to look. Others are peeping too, although most are still covering their eyes or looking away from where the witch was standing.

Mrs. Egin is gone. Nothing of her remains, except a circle of blood and grisly carnage, covering the grass, Logan and many of the children. And at the centre of the circle - a panel of greyness.

The large grey patch of light hangs motionless a foot or two above the ground. It's three or four feet wide, maybe six or seven high. Jagged round the edges.

I'm not the only one who can see this light. Others are pointing at it, gasping, murmuring, "What the hell is that?" This is a different type of light from the ones I usually see.

Logan rises, rubbing his head. Stares in disbelief at the gory mess, then at the grey wall of light. He's an educated, experienced man. But he's seen nothing like this before.

"She exploded!" a boy yells, excited. "Did you see her? It was amazing!"

"Is she dead?" a girl asks, voice trembling.

"What's that light?"

"Yeah, what is it?"

"Yeah."

Logan walks round the panel of light. I can only see his feet when he's behind it. Then he comes back into view. He's more bewildered than afraid, like most of the kids around me. The light has made more of an impression than Mrs. Egin exploding! Perhaps they're in shock, not ready to deal with the explosion - and her death - yet.

"We have to get away from here."

I hadn't meant to speak, but now that the words have popped out, I know I'm right. Everybody gawps at me. "This is bad!" I shout. "That light's dangerous. We have to run."

"It's OK, Kernel," Logan says. "This is mind-blowing, but we're in the midst of something wondrous. I'm not sure what's going on, but this is a once in a lifetime opportunity to experience the miraculous. Mrs. Egin... this light... it's incredible!" He beams with delight.

Some kids get to their feet and drift towards Logan and the panel of grey light. They're not afraid now that Logan isn't. They trust him. They think he knows best.

"This is wrong!" I yell. "It's evil! Can't you feel it?"

"You shouldn't be so suspicious, Kernel," Logan laughs uneasily.

"You're covered in blood!" I roar angrily, unable to believe that someone so smart can be this stupid. "Mrs. Egin's dead! You're walking through her guts!"

Logan blinks. Looks down at his blood-soaked shirt and trousers. His red hands. The mess around him. "Oh," he says quietly. "Oh my - "

Something bursts out of the grey light. It has two long legs, a stumpy, leathery body, four arms which end in thick, hairy fingers. A dark green head, a cross between a human's and a dog's. No mouth. Long draping ears. Wide, white, evil eyes.

The thing grabs Logan. It somehow makes a hissing, whistling noise. Logan stares at it in shock. Two of its hands lock on his head. The others clasp his shoulders. The hairs on its fingers extend, growing at an unnatural speed, digging into the flesh of Logan's face. One hair darts into his right eye, puncturing it. Logan shrieks with pain.

Then the thing's upper arms jerk apart quickly - ripping Logan's head off his neck! The monster tosses it to the ground. Stamps down hard with its right foot. And Logan's severed head pops like a melon dropped from a great height.

The thing looks at the rest of us. Spreads its arms and hisses. And thirty-four kids scream as one and crap their pants.