The school was bustling with hallucinations, or ghosts, or whatever they were. They were in their other uniforms, ignoring me, all getting on with their lives. I tried not to think of the colour blue, but that made it fill my mind and they all started to shine.

I’d never seen so many at once before. I forced myself to look hard while I had the chance. I could see now that their sweatshirts were burgundy, and that they were allowed to wear trainers, even branded ones.

I watched two girls talking. They weren’t floaty ghosts: once you filtered out the blue they were just girls. I saw two boys standing next to each other. One was searching through his bag for something. I saw a tall girl eating a bag of crisps on her own, leaning against the wall.

They didn’t seem to be from the past. If they were from the future that meant that they weren’t ghosts.

It meant that if anyone was a ghost here it was me.

Was I haunting these people? Could I be the ghost?

‘Ariel?’

It was, of course, Ms Duke, standing behind me.

‘Sorry,’ I said. ‘Running a bit late.’

‘Everything OK?’ She gave me a searching look. ‘You don’t look as happy as I’ve seen you, Ariel, if I may say so.’

‘I’m all right. Honestly.’

I worked very hard on those words being true. I wanted to be all right. I couldn’t bear to be stopped in my tracks by a bunch of blue people who weren’t really here.

It would be worse, though, to discover that I was the one who wasn’t really here. Could I be dead? I didn’t think I could. If I was dead then I’d be with Mum. Or she’d be here with me.

Ms D was looking at me. I tried to imagine telling her. She might help. She was one of the few people I pretty much trusted. She was waiting for me to say something more.

I looked back at the ghosts. They were still there, walking around, chatting to each other, but I couldn’t hear anything. They were more like people on telly than anything else, if the telly was on mute. It was as if I was watching a programme set in a school, on a TV whose colour had gone strange, playing out in 3D against the backdrop of my real school.

Ms Duke clearly wasn’t seeing them.

‘I’m all right,’ I said with more enthusiasm this time. ‘We ate healthy food all weekend and did some housework.’