Even though it’s June, and the rain has stopped, there’s a bleakness about Whitley Bay’s seafront that makes it seem like it’s permanently February. Perhaps it’s the boarded-up hotels that look like they were once grand, but now remind me of the old people in Great-gran’s home: crumbling and unloved.

Perhaps it’s just my mood.

Why is it, I ask myself furiously, that these twins seem to make everything worse?

The rain has given way to a clear, cool evening, and the seagulls have fallen silent. A weak sun is starting to set behind us, giving a pinkish tinge to the lighthouse.

We head down to the Links. Bang in the middle is an old, flaky bandstand.

Jesmond and Jarrow are already there, watching us as we approach.

‘So … what do we say?’ I ask Boydy, who has developed this strangely calm manner that I’m finding unnerving.

‘Relax, Eff. We deny everything. They can’t have any proof at all.’

‘They’ve got a video – that’s what their message said,’ I say.

‘Yeah, well, even if they do, it’s not going to show much, is it?’

‘Hmm …’ My mind goes back to Jarrow filming on her phone. I can’t share in Boydy’s confidence. ‘So what are we going to do?’

‘We just bluff it out and tell ’em to go to hell.’

‘We could have done that by text. Why are we meeting them?’

‘Well. We want to see exactly what it is that they’ve got, don’t we? Just in case. Assess the evidence before comin’ to a verdict an’ all that.’

We are a few metres from the bandstand now.

‘OK, just let me do the talking,’ Boydy says.

‘Get stuffed. I’ll talk if I want to.’

‘Fair enough, Effow.’

We step up into the bandstand where the twins are waiting. Honestly, if I wasn’t so tense I’d have to laugh. They’re both standing there, feet apart, arms folded, like they’re posing as a pair of sinister, blond Bond villains.

They nod at us curtly.

‘Evening, Jarrow. All right, Jesmond?’ says Boydy.

‘A’reet, Boyd, Ethel,’ says Jesmond. (The boy twin. Don’t worry, I used to confuse them all the time. And, incidentally, ‘Boyd’? That’s just blatantly intimidating. No one calls him by his last name – at least, not without a ‘y’ added, and that’s only me, I think.)

I straighten my back, and refuse to be intimidated.

Jarrow says, ‘It’s nice to see you, Ethel. That is, to see all of you.’

I don’t reply. It seems like a good strategy: say as little as possible so as not to give anything away.

There are wooden slatted benches encircling the bandstand, covered with graffiti and with a snowdrift of litter gathered underneath.

We sit down, and Jarrow continues.

‘Y’see, it all makes sense now. Well, sorta. That day we found your dog for you, we thought there was summin’ up wi’ yer hand, didn’t we, Jez?’

Jesmond nods.

Jarrow blinks hard behind her glasses. ‘Like, we couldn’t see it when we shoulda been able to.’

I look down at both of my hands and turn them over, as if to say, What’s wrong with my hands?

Jarrow ignores this. ‘And then today at the School For Show-Offs. That thing wi’ your guitar. Fishin’ line? Are you kiddin’? Ah know a bit about fishin’ and there’s not a line in the world that’s thin enough and strong enough to do that.’

I glance over to Boydy, and our eyes meet. He’s chewing his bottom lip.

‘Anyway,’ she continues, ‘we heard yuz. Well, you anyway. “Catch, Boydy!” Definitely your voice, and all caught on camera!’

It’s like they’ve rehearsed it. At the mention of the camera, Jesmond pulls out a phone. In a moment he’s brought up a film, and I lean in to watch with a mounting feeling of sickness.

It starts when Boydy begins his walk down into the audience, the guitar floating in front of him. The footage is wobbly, but it’s still a terrific illusion. I was worried that somehow the camera had ‘seen’ me in a way that the human eye cannot – that it would see and record light in a slightly different way, and that somehow I would be visible – but no.

I am as invisible on the camera as I was in real life.

There’s the noise of the audience, and then the chaos starts. People pushing their seats back with a squeak; Mr Parker telling everyone to sit down. Then the image tilts wildly as Jesmond hands the phone to Jarrow, before fixing on Boydy coming ever closer.

And the water.

For a brief second after it hits me, the water creates the outline of half of my face before running off and dispersing. You can’t really tell what it is. I start to allow myself to hope that I have been worrying for nothing.

And then my voice: ‘Catch, Boydy.’ I must have said it very close to the camera’s microphone because it’s very clear. Unfortunately, it’s also unmistakably me, but so what?

Then the scene changes. It’s a few seconds of film, shot from the school reception during the downpour. You can hear someone saying, ‘There! Did you get it?’ and there’s the slightest blur of something moving away and round the corner, but you can’t tell what it is.

I’m working on a little half-smile, bordering on a sneer. I’m going to turn to the twins and say, ‘Is that it? Is that the best you can do? That proves nothing other than you two being a couple of crazies with fantasies of invisible people. Got any leprechaun films as well? Ha! Losers!’ Or something to that effect, anyway.

But my sneer is frozen, half formed.

Because the film is now repeating, in slow motion. At the point the water hits the side of my face, it slows again, to a frame-by-frame rate. That’s when it’s clear. Unmistakable, in fact. My face, or half of it at least, outlined in water.

Just for a few frames. You’d miss it otherwise, but slowed down, there’s no question.

The slo-mo and enlarged version of the film shot in the rain reveal even more.

There I am. Almost completely transparent, but outlined by the torrential rain, running away from the school’s lobby. It’s definitely a person. A half-invisible, naked person.

Definitely me, in fact.

That’s where the film ends, and Jesmond replaces his phone in his pocket.

‘It’s you, isn’t it?’ he says, and he’s the one smirking now.

Boydy and I exchange glances but neither of us says anything.

‘It’s pointless denying it. You can tell it’s you. It’s obvious from the way you run. Besides, it was your thumbprint that was used to open the school gate.’

Boydy goes on the offensive. ‘Rubbish! You don’t know anything. How the hell can you know it was her thumbprint?’

Jarrow chips in now. ‘Easy, if you’ve got a little bit of leverage over Stuart in Security. A little bit of persuasive power, if you know what I mean?’

Old Stuart Hibbert is the night security guard. He’s a nice guy who doubles up as a lollipop man on the busy crossing at the back entrance.

‘Old Stuart? What on earth has he done?’

‘Not for us to say, is it, Jez?’ says Jarrow. ‘But let’s just say fifty quid goes a long way when you’re a security guard on minimum wage.’

‘You bribed him?’

I can hardly believe what I’m hearing. Basically, the Knight twins have paid the school’s nightwatchman to hand over security information.

All four of us are so silent that the only sounds are the competing swishes of the traffic on the road and the sea on the sand.

Jesmond Knight speaks first. ‘So, I’ll admit this much: we’ve got no idea what’s really going on. But it seems to me that you,’ and he jabs his finger at me, ‘have got some weird invisibility thing. Is it a magic spell? Is it some sort of suit you put on? Is it some military thing? Haven’t a clue. But I’ll bet it’s top secret, and I’ll bet you want to keep it that way. Otherwise we’d have heard about it.’

I’m glaring at him while he says this. He is, of course, more or less spot on, and I’m terrified.

‘So here’s the deal,’ says Jarrow. She takes a long pause while she removes her glasses and polishes them with a hankie, making us wait. Finally, she says, ‘It’s on Jez’s phone right now. That’s where it’ll stay so long as you play nicely. Or should I say, pay nicely.’

‘Pay?’ says Boydy.

‘Oh aye. We reckon a thousand quid should do it, don’t you, Jez? It’s manageable, if you do it in instalments.’

I feel sick. Not just upset, but really sick, like I want to throw up.

A thousand pounds. Where would I get that?

‘You’re mad,’ I say eventually. ‘There’s no way we could get anything like that amount. No way at all.’

I’m furious, but I’m also very scared, not to mention utterly stunned. This is proper blackmail. Not behind-the-bikeshed-stealing-your-sweets stuff, but the sort of thing that real criminals do.

‘It’s not a negotiation. You realise that, don’t you, Little Miss Invisible? It’s not like we’re going to haggle.’

‘I can’t do it.’

He shrugs. ‘This is the sort of thing that goes viral instantly. A couple of calls to the Evening Chronicle, you know? “Local Girl’s Invisible Secret.” All over YouTube, easily. There’ll be reporters camped outside your house. You’ll be Invisigirl from The Incredibles, only in real life, you know? And it’ll stay with you for ever, Ethel. Stuff like this never goes away.’

‘Get stuffed.’

The words come out, but – maddeningly – they wobble in my throat. Somehow, the Knight twins have zoned in on my one big fear. They’ve worked out that I’d truly hate to be famous like that, and they’re going to exploit it.

‘Have it your way.’ Jesmond takes out his phone and mutters to himself as he prods the screen. ‘OK … upload … preparing to upload …’

‘Stop!’

He stops, finger hovering over his phone, his face a picture of innocence. ‘Yeah? What?’

‘Give us time. Time to think.’

The twins look at each other, and they both nod. Jesmond puts the phone away.

‘OK. Three days. See yuz. Well, not you, obviously,’ he says, pointing at me. ‘Not if you’re invisible anyway.’

Without looking back, they saunter off, laughing at Jesmond’s joke, leaving me and Boydy in shocked silence.