There is a reservoir not far from the cottage: I have been careful not to visit. It calls to me in my dreams and I can smell its dampness on the air on days when the wind blows in the right direction. I try not to think about it. I don’t take baths. When the kettle boils I can’t watch the bubbles clawing at the plastic window.

I’m not prepared for the Thames. I’ve been avoiding water, however it comes, and here it is. Thick, fast-flowing, surging beneath me as I cross the bridge. Even without looking I sense the river’s power. The sun flicks at the corner of my eye, reflected from its surface. Butterflies stir my stomach.

Halfway across the bridge I stop walking and stand at the railing. I grip the bar tight, so the veins in the backs of my hands bulge. I’m getting funny looks. The trains behind me clatter over the water towards Charing Cross. Breathing deep, I examine the subtle topography of the waves, and a plastic bottle being sucked along by the current.

I shake my head and force my body away from the barrier, carry on walking, somehow reach the north embankment. My jeans are chafing my thighs and my belt is uncomfortable at my waist.

I am early, so I browse the market in Covent Garden. There is nothing I want. All the same, I buy a glass paperweight – a kind of clear ball with a blue core that looks liquid but isn’t. Like a wave, frozen.

Even after all this time the dry notes feel alien in my fingers.

‘Ta, sir,’ the stallholder says when I tell her to keep the change. I have had to repeat myself several times for her to grasp the words under my accent. I stumble on the cobbles, but catch the paperweight before it can fall and manage to stop myself before I am on my face. The bruises are something you get used to.

Sylvia is sitting in the window. If she notices me through the glass she doesn’t show it. Our meeting place is a kind of juice bar on the ground floor of Marks and Spencer, the kind of place where tourists drink lattes and expensive milkshakes. I buy a bottle of juice and take the vacant stool next to Sylvia. She sips cola through a straw and keeps her bleak eyes on the glass.

‘You’re early.’ Her accent is much like mine.

‘So are you.’

It’s been five years, give or take a month, since we arrived, together. The first few weeks are a bit of a blur. I haven’t seen Sylvia for four of those years. She looks well. Hair the same bright platinum it’s always been.

Our skin is the same grey. We look like a couple of corpses, I think, sitting here, staring out onto the street, sipping our drinks through straws.

We watch the people outside the window. This portion of Long Acre is a popular meeting point. People line the space in front of the glass, waiting. A busy zebra crossing holds up a queue of black taxis. The tube station spits out a wash of tourists every couple of minutes, every time a lift reaches the surface.

‘Things are so funny, aren’t they?’ I say.

Sylvia says nothing.

I slide the brown paper bag from the market to her. ‘A gift.’

She peers inside without touching it, as if suspicious.

‘What am I supposed to do with that?’ she asks, pushing it back to me.

‘It’s a paperweight. It stops paper blowing away on the breeze.’

‘I know what it is,’ she says. ‘Paper is the epitome of dry. I don’t like it.’

I nod. We sit in silence.

‘Have you been alright?’ I ask eventually. It’s so much less than what I want to say, but it’s the closest approximation this language can allow.

Sylvia shrugs.

‘You’ve got a place to stay? Money?’

She nods.

More silence while we both suck on our straws. Sylvia still hasn’t looked at me. I want her to make eye contact. I know if she did I could get a sense of how she really is. There is another language, one that doesn’t need words.

‘Did you bring them?’ I ask.

‘I’m here, aren’t I?’ Sylvia looks at me now, self-assured and confident. Her eyes tell me she is settled. More settled than me, anyway. I wonder if she has something like a family. ‘Before I give them to you I need to know what you want them for.’

I sigh. Anything but this. I take a deep breath.

‘I’m going back.’

She shakes her head. Her lips tighten. ‘You need to let it go.’ But I can tell she’s hopeful, a part of her thinks I’ve found a solution, thinks I already know how I’m going to do it.

‘No,’ I say. ‘I won’t. I’m sick of all this.’ I gesture, trying to indicate the people, the queues, the building itself, the air. Everywhere there is air.

‘And how will these help?’ she asks, pulling a small, white envelope out of her bag.

‘I thought you didn’t like paper,’ I smile.

‘Sometimes it is necessary,’ she says. ‘What are you going to do with them?’

They’re so close. I could reach out and touch them. Grab them even. Grab them and try to run.

‘You’ve heard of genetics?’ I say instead, ‘DNA?’

She glares at me.

‘Just checking,’ I raise my hands in defence. ‘I’ve been learning about it. Double helixes, base pairs. Nucleotide sequences.’

Her eyes widen. ‘Have you told people?’

‘I’m not going to be able to do this on my own.’

‘You’re risking everything, all our secrets for...’ Incredulous, she thinks for a moment. ‘That’s just like you.’

‘They’re not oursecrets anymore,’ I say. I hold out my hand. ‘Give me the envelope. Either you give it to me or I take it. If you’re anything like me you can’t run all that well, so don’t even think about trying to get away.’

Sylvia stares at me. In my head I can hear her name, her real name. It is beautiful. Sylvia doesn’t do her justice. Doesn’t come close. When you lose your language you lose part of yourself. We are different people here. We’ve lost our words, our names. We lost everything on that beach, one night five years ago, give or take a month.

‘Alright,’ she sighs. She hands me the envelope. ‘Just, please, be careful.’ She stands and starts to leave, tossing her bag on her shoulder and lumbering heavily to the exit without saying goodbye.

Then she turns and walks back to me. ‘If,’ she says, ‘by some miracle, you do find a way back,’ she pauses, ‘don’t you dare go and leave me here.’ And then she kisses me, like I’ve seen on the television, and for a moment our tongues are together, wet and alive and for a second I think we have found another language. But then she’s walking away.

The envelope quivers in my hand. I examine it. It isn’t sealed and I pull it open.

I’d forgotten how small they were. There are only six of them. The rest washed out to sea. They are thin and silver, like glass.