I keep walking. I want to go faster. It’s impossible to run in the two foot of water between each threshold, but I wade as quickly as I can, my arms out by my sides for balance, like an insane windmill. At the same time, I don’t want to trip. I have to navigate. I have to stay upright. I have to get to my dad. I trudge through this watery submerged cathedral under Finsbury Park and I try not to be afraid.

I am three or four arches from the end of the tunnel when the lights go out and I’m plunged into complete darkness. The light from behind me, channelled down from the hatch space, has disappeared. Fear grips me like one of those brittle, plastic skeleton hands on the ghost train. Has someone closed the hatch? Those boys, laughing as they trap the ugly creature in the dungeon, have they shut it on me? Bloody hell. It’s pitch black. I’m scared to go any further; then I remember I’ve got my phone. Doesn’t it have a torch? I’ve never used it before but I know how to put it on. Shit, one per cent, I think, looking at the screen; I haven’t charged my phone since this morning. I flick on the torch and angle the phone in front of me, to light my way.

‘I’m almost there, Dad!’ Through the water, over the threshold, each arch in turn. It’s getting cooler and cooler. I can feel the hairs on my arms begin to stand to attention. I splash through the water, the light from the torch reflecting from its surface. One arch to go, though, and everything goes black again, as my phone conks out. Absolute velvet pitch darkness.

Oh, fuck. Where’s Paddington when you need him?

‘Dad, say something again so I know exactly where you are!’

‘I’m here, love. I’m here.’

He’s to the right. He’s beyond the final arch. I’m relieved I’m so close to him now, but I’m frightened. It’s so densely and relentlessly black. If he can’t walk, how am I going to get him out of here, in the dark? How will we even find our way out when neither of us can see? I clamber over the last brick threshold, slick and a little slimy, feeling I may trip at any moment. I wade into the final pool of water.

‘Dad?’

‘Here!’