But he’s ten. The fight for his soul isn’t lost yet.

I turn us around again, and once more we lurch across the cellar. My son deserves the chance to live. The better angels of his nature deserve the chance to win. I’m not going to let what happened here in this cellar with Stacey be the sum of who he is.

‘I’m hungry,’ Peter says.

‘Try not to think about food,’ I say.

He sags against me. ‘But I can smell McDonald’s, Mummy.’

It’s not McDonald’s he can smell: it’s woodsmoke. Someone must be burning autumn leaves in one of the gardens nearby. Air is getting into the cellar from somewhere. And if air can get in—

I tell Peter to keep moving, and clamber onto the top of the chest freezer. The air is cooler near the ceiling, and I hold up my good hand in the dark, trying to feel where the faint breeze is coming from. If it’s the hatch I saw above the pool pump, there’s a chance Peter could scramble through it: he’s slight and agile.

Inching carefully along the slippery lid of the freezer, I lean out above the pump cage. This is definitely where the air is coming in: I can just about reach the edge of the maintenance hatch above the pool pump with my fingertips. But it’s so small. It’s not designed for someone to access the cellar, merely for a mechanic to be able to reach in and fix the pump if required. It can’t be more than thirty centimetres in diameter at most. Even if I’m able to prise it open from the inside, I don’t know if Peter can wriggle through it. I’m not even sure I can lift him up high enough to try.

I climb back down and feel my way across the cellar in the dark. I need something to stand on so that I can reach the hatch properly and try to open it.

‘Stay where you are a moment, Peter,’ I call. ‘I have to move a few things.’

There’s an ugly thump when I roll Felix’s body onto the floor, like the sound of a bag of flour splitting when it hits the ground. I flinch, but I don’t have time to dwell on it. I drag the metal bed frame across the cellar in the dark, praying the sound of the legs screeching across the concrete floor doesn’t carry.

‘What are you doing?’ Peter asks.

‘Trying to get us out of here,’ I pant.