I don’t really have any choice, do I?

I have not exactly picked the best time to wander through the school naked, though, because as I open the door from the girls’ bathroom, the bell goes and about half a dozen classes start emptying their students into the main corridor, as well as the audience for Whitley’s Got Talent.

There are two ways I can go: back through the Performing Arts Block, or follow the main corridor along to the big glass-walled reception area, which is already filling up with students.

I consider waiting in one of the toilet cubicles until the break is over, but the tingling on my skin is intensifying, and – based on the last time – I figure I have five minutes tops to make it back under the rhododendron bush to retrieve my clothes.

I check myself one last time in the mirror, and remove a crust of blood from my nose.

‘All clear,’ I say to myself, and then – despite my nerves – I smile. Because that’s what I am: like a glass of water, I’m all clear.

I’m out of the bathroom door just before four sixth-form girls barge in, and I narrowly avoid a second collision.

From now on it’s a race against people and my soon-to-expire invisibility.

Dodging and weaving through the mass of bodies, I make my way down the corridor. I bump into people; I knock their bags. Some turn round and say, ‘Hey! Watch it!’, but there’s enough of a crowd for no one to be quite sure who bumped them.

In reception, the rain is hammering on the glass roof and I’m immediately gripped by my old fear, but now it’s bordering on panic.

Stop it, Ethel. Not now, not now, I tell myself.

I dodge behind a large potted fern where I’m kind of out of the way, and I take deep breaths, digging my nails into my palms until they are sore, and that distracts me from my fear.

I need someone to open a door so that I can squeeze through. Trouble is, no one is going outside. Why would they? It’s bucketing down.

My head is throbbing, and my skin feels like a million ants are crawling beneath the surface. And …

Oh no.

No, no, no.

If I peer really closely at my hand, I can see the faintest beginnings of a shape.

A minute? Less? Until I’m actually living the world’s most common recurring nightmare, and I’m naked in public.

I swallow. I take a deep breath and then …

I. Just. Run.

I’m at the side door in a second and I push it open. It seems like a hundred pairs of eyes turn to the noise of the door slamming back on itself as the rain gusts in.

Someone says, ‘What’s that? Look!’

I’m out and running through the rain.

I can see the raindrops hitting my arms and legs and forming a brief translucent outline that shifts and changes as I move.

In twenty metres I can turn a corner past the Science Block and be out of sight of the people in reception. Before I turn, I look back: faces are pressed against the glass walls, and some people have come through the door that I left open, trying to get a better look at this ghostly shape moving through the rain.

And now I’m round the corner and heading to the main gate. It’s shut.

The only thing I can do is open it with my thumbprint and deal with any consequences – whatever they could be – later.

I can just see my transparent thumb as I press on the sensor pad. The gate swings open and I’m through, ducking under the rhododendron leaves to safety.

I’m done in, and I just collapse, flat on my back among the dead leaves and cigarette ends. I can hardly breathe, my brain feels like it’s going to explode, and I screw my eyes up before I roll over and throw up.

Then I sit up and look down.

I look down at me. I’m here; I’m back. There’s my thigh. Here’s my hand. I close my eyes and everything goes black, just as it should.

I’m visible.

I retrieve my plastic bag from where I left it, get dressed, and wait under the dripping rhododendrons until the rain stops, leaning back against a metal pole.