“But I need to peeeeee!” I insist, dancing on the spot and trying to show the playground supervisor how urgent my case is.

“You were supposed to go before you came out! There’s only another ten minutes of break left, can’t you wait?”

Miss Finlay doesn’t like us going in and out at break time and ‘getting up to mischief’, as she calls it, but one look at my pained face is enough to confirm I’ll cause way more trouble if she doesn’t let me back in.

“Fine, come straight back out though, do you hear me, Jamie? No detours or mucking about at the water fountain.”

She swipes her keycard to open the security lock, and I run back in to go to the loo before my bladder explodes. I don’t know why I’m so desperate to pee – I was so busy setting up my science display this morning I didn’t even remember to fill up my water bottle.

It’s still sitting on my desk.

My classroom’s not that far from the boys’ toilet and the water fountain. Maybe I should just fill it while I’m here…

I run back to class and fetch it, nearly knocking the janitor down in the corridor and spilling water on the floor when I hold my water bottle the wrong way up.

“Jamie, shouldn’t you be outside?” The head teacher frowns at me as he walks past. He’s taking three people to the staff room. They look important. They must be the science fair judges.

For one mad second I think about bowing to them like they’re royalty, and then I have to clamp my hand over my mouth to stop myself laughing out loud at how funny that would look.

“I’m just going to the toilet,” I mumble through a mouthful of fingers, and then I run off before I can get into trouble for turning the corridor into the River Clyde.

We’re doing a project about Scottish rivers in class just now. It’s not as much fun as the Vikings, but that’s only because Miss Morrison didn’t listen to my suggestion about making a model Viking boat to go sailing on the Clyde. She said we’d already made a boat, and I said the cardboard boat stuck on the wall was a bit rubbish, and she said I was cheeky and I’d get extra homework if I wasn’t careful.

Why isn’t it cheeky when Miss Morrison tells me my handwriting’s rubbish then?

Maybe I should give her homework when she makes me rewrite my science reports.

She’s in a good mood with me for once as she thinks my science fair entry is brilliant, even though the writing on my cards is all over the place. I’m so nervous and excited and worried all at the same time at the thought of winning that my stomach feels like I’ve swallowed Elin’s whole butterfly display in one gulp. The judges will probably pick her entry, even though it’s not a proper science project, just a lot of pretty pictures. Everything about Elin is pretty, from her neat handwriting and super-clean clothes to her stupid painted pottery collection. Teachers love her. They think she’s perfect.

They don’t know she tells lies and says hurtful things when they’re not listening.

She’s not so perfect on the inside.

Not like Paige.

I’m playing with the taps and feeling bad that Paige is avoiding me after all the times I lost my temper and yelled at her, when Steven puts his head round the door.

“Didn’t you hear the bell, Jamie? Break time’s over. Miss Morrison’s looking for you. She says you have to come right now!”

He looks excited, like he knows something he’s not telling me.

I wonder if it’s something bad, and the sick feeling in my stomach gets worse when he leads me down the corridor to the assembly hall instead of back to class.

“Is the judging finished already?” I ask. “That was quick!”

Steven shoots me a look that’s half nervous and half sympathetic. It’s the kind of look you give someone when their pet dog’s been run over and you don’t want to be the one to tell them. But I don’t have a pet dog, so I don’t know why I’m getting the look.

“The head teacher wants all of us who entered the science fair competition to come to the assembly hall,” he says, without really answering my question.

Steven’s got a pet dog. Maybe it’s his dog that’s been run over.

There’s lots of teachers and a bunch of classroom assistants in the hall. They should all be in class now that break time’s over, and Mr Conway the head teacher should be in his office eating Hobnobs with his super-important guests. He’s not though. He’s standing there with his hands on his hips staring at me like I’m the driver who’s just run over Steven’s dog.

“Jamie, why would you do this?” he asks. “What were you thinking?”

“Do what?” I blink. “I haven’t done—” And then I see what they’re all looking at.

My display’s been completely smashed.

The table’s lying on its side and the crystals have been trampled so hard into the floor all that’s left of them is piles of coloured powder. My rock candy tree’s been pulled apart and the boiled sugar lollipops are strewn around in bits. The display cards I spent so long writing have been ripped to pieces and the photographs are all torn.

There’s nothing left of my entry.

I’m not going to win a place at the science fair now.

For a long moment I can’t speak. All the air’s been sucked out of my lungs. I stare back at Mr Conway with my mouth open, waiting for him to tell me it’s all just a big joke.

He doesn’t. He just asks again, “Why did you do it, Jamie?”

“I didn’t!” My voice doesn’t come out above a whisper. “It wasn’t me.”

“Don’t lie, Jamie, not about this.” Miss Morrison’s towering over me with her badger hair and coffee breath, and I’m so full of rage I can barely keep the peanut butter toast I had for breakfast down. “Miss Finlay let you back in at break, and the janitor saw you in the corridor just outside.”

“I saw you myself,” Mr Conway says. “We’ve asked all the other boys and girls and you were the only one in here at break. Why would you destroy your own experiments, Jamie? It’s completely senseless.”

I look round the hall like I’m searching for someone to rescue me, but no one offers to help. Paige isn’t here. She isn’t entering the science fair. Her mum can’t afford to buy any craft stuff. She can’t save me from the ten-ton bomb of rage that’s ticking down to zero in my head. Everyone’s staring right at me, waiting for me to explode.

Everyone except Elin.

Her eyes are on the floor, and she’s clenching her hands so tight her knuckles are white. Today she isn’t hard to read. The guilt’s written all over her face.

Her betrayal hits me so hard I nearly fall over.

“It was Elin!” I gasp. “She did it!”

Elin’s head snaps up, her cheeks flaming red. “Of course I didn’t!” she says, too quick and too loud. “I’d never do anything like that.”

“She’s lying!” I yell. “She’s the one who ruined everything!”

“Elin doesn’t lie,” Miss Morrison frowns. “I’m afraid you’re the one with the history of that, Jamie.”

There’s no way for me to win. Elin has them all wrapped so tightly round her little finger she could pull my experiment to pieces right in front of them and they’d still think it was me. I can’t believe they’re so blind. I can’t believe I’ve been so blind.

I thought if I was nice to her for long enough she’d stop hating me and we could be a real family. I spent weeks working on my science project so I’d have a chance of winning enough money to buy her riding lessons and make her dreams come true. I forgave her even though she lied to Miss Morrison and Dad and Liz about me time and time again.

I even trusted her with my medication every morning.

Wait.

My medication…

I’ve been feeling all wrong for weeks.

Ever since Elin started giving me my medication instead of Liz.

The time bomb of anger goes off, and all of a sudden I’m screaming and crying and lashing out at the classroom assistants who try to stop me reaching Elin’s butterfly display.

I don’t want their sympathy or their soothing words.

I want revenge.