In the Dream City, everything is in colour except for the people. They are in greyscale. As I get closer to the gap in the fence, I see that greyscale people are queuing up to climb through a hole in the floodgate and then stepping through the chain-link fence. They appear to be adults and children, but they are all wearing masks so I can’t see their faces. One at a time, they climb through the gap in the fence and keep walking, right off the edge of the bank and into the river.

Their heads disappear beneath the turbulence.

There are no boats in sight. There are no life rings.

I hurry forward. I shout, trying to get people’s attention, but no one even turns their head. When I reach the gap, I stand there and try to block the next person from coming through, but I can’t.

‘Hey!’ I cry. ‘Don’t go through here. You’ll fall in the river. Look where you’re going!’

The person ignores me and steps around me. I even grab his arm to try to stop him.

‘Don’t touch me,’ he says in a dull voice. ‘It’s assault.’

Startled by the accusation, I hesitate – and in that time he walks straight off the edge of the muddy bank and into the deep water. He disappears.

I try to block the next person. They are wearing a plastic doll mask with eyes closed. I grab the edge of the mask and rip it off. Underneath is another mask with eyes closed.

What the hell? There is no way these people can see where they are going because the masks have no holes where the eyes should be.

‘Wake up!’ I scream. ‘Wake up!’

The person faces me and tries to walk through me.

‘Where are you trying to go?’ I say. ‘This is the river. You’re going the wrong way.’

In a tinny voice, she says, ‘I’m going to a Sleepwalkers Anonymous meeting. This is the right way.’

Then she reaches out and pushes me. I fall.

There’s a muddle of sky and lights and reflections before I hit the water and go under with the whole river punching down my throat like a cold fist.

Cardboard box in Wandsworth Town

I don’t so much wake up as crash into reality. My mouth tastes like rancid goat and I can feel the headache still lurking like a bank of thunderheads on my internal skyline. Sometimes I get a touch of synaesthesia, so when I smell nail-polish remover I expect it’s connected to the headache. Until I open my eyes.

I am home in Finsbury Park on the sofa. O is sitting on the recliner opposite in her dressing gown, her hair in rollers that she must have slept in. Her wheelchair is parked nearby and she has put her bare feet up on it. With her reading glasses on the end of her nose, she looks like a plump, wrinkled elf as she paints her toenails a lovely turquoise. Outside, the sun is coming up over North London.