I have hardly slept at all.

(I don’t think you would, either, if you had to do what I have to do this evening.)

I was kept awake by another rainstorm. It’s turning into one of those English summers that you get in the old comedy films that Gram likes: that is, the unfunny ones where people go on holiday to resorts like Whitley Bay used to be, and it rains just as they’re putting up their deckchairs.

Anyway, all night I was torn between thinking, Please stop, rain, please stop and Rain as hard as you can so there’s none left tomorrow.

Rain, as I discovered at school, is not a good companion to invisibility.

As for explaining why I’ll be out all evening, this has taken a bit of thought. In the end, I settle on a text to Gram, which I send to her during morning break.

Boydy’s having a gathering tonight for his birthday. Movies and pizza. His mum will drive me home. Back by 11. Don’t wait up. E xxx

Normally – that is, with Gram behaving normally – a text like that would produce an avalanche of further questions, probably starting with ‘What on earth is a gathering, Ethel? Is it like a party?’ But lately, I’ve begun to trust that Gram will react anything but normally. It’s kind of like ‘expecting the unexpected’.

She texts back:

Will there be others there?

Easy.

Yes, there will be about seven of us.

Plausible? I think so. So does Gram.

All right. Have fun. X

I’ve been staring out the window during the physics lesson, gazing at the flat, grey sky and trying, by force of will, to ensure it stays dry. Soon, I’m practically falling asleep, even though the subject is very close to my heart: the nature of light.

‘I hope you all understand this,’ says Mr Parker. ‘There’ll be a test at the end of term, you lucky duckies.’

Groans all round.

Light is energy, I’ve got that.

It’s a type of radiation – the type we can see, because our eyes have evolved to be able to see it.

Then Jesmond Knight puts his hand up. He’s in the same class as me, but his sister isn’t.

‘Mr Parker,’ he begins, and then he turns his head to look straight at me. ‘Do you think it’s possible for a person to be invisible?’

‘I’m over here, Mr Knight, thank you. Do you mean like Harry Potter’s cloak of invisibility? Or the one that occurs in the legend of King Arthur? Or the “cloaking device” in Star Trek? A splendid question, and the answer is – get ready to have your gobs smacked and your flabs gasted – yes! In theory, at least. You see, researchers have been working—’

Jesmond interrupts him – always a dangerous move with Mr Parker, but he gets away with it. ‘Sorry, sir. I didn’t mean that. I meant the whole person.’ Again, he turns and looks at me, a sly smile on his face that doesn’t reach his eyes.

‘Ah! An invisible person? Well, that would require both biological and technological breakthroughs that have so far proved elusive to even the finest minds in science. So the answer to your question, Mr Knight, is – for the time being at any rate – a disappointing and resounding “no”. Continue with this inquisitiveness, however, and you may yet be the scientist who makes the discovery that—’

‘So, sir, if someone had the ability to become invisible—’

‘That is a BIG if, Mr Knight.’

‘I know, sir, but if they did, they’d be, like, famous an’ that?’

‘I very much expect that indeed such a person would be, like, famous an’ that. It would be a worldwide sensation without a shadow of a doubt. And talking of shadows, who can tell me the difference between the umbra and the penumbra of a shadow? Yes, Miss Wheeler?’

And he’s off again on the nature of light, leaving Jesmond smirking at me in the most creepy way. It makes me feel sick.

People are still talking about the strange events of Monday:

• Rafi McFaul tells me I missed the freakiest thing, like, evah, even though she didn’t see any of it, while those who do claim to have seen something – mostly people in the foyer who were looking out at me running through the rain – are exaggerating their accounts alarmingly.
• Sam Donald says he saw the ‘ghost’ (for this is what I am becoming) turn and laugh, pointing at someone in the crowd.
• Anoushka Tavares insists it was not the figure of a human, but something larger, like a big ape.

I have to hand it to the Knight twins: they must have incredible willpower not to just show everyone their film. But they’ve only given us till the end of tonight to make the first payment of money we don’t have, and once they go on that school trip there’s no way they’re not going to end up getting out the video when everyone’s around the campfire or whatever.

It all makes it even more essential that I act now.