Peter’s room is unnaturally tidy for a ten-year-old boy’s. His bed is made, his few toys neatly put away in the correct storage bins: he never showed much interest in traditional playthings like Lego or cars, so eventually Tom and I stopped buying them. He’s always enjoyed taking things apart – breaking them – but he’s never shown the slightest inclination to put them back together. He has a fondness for collecting pieces of junk: circuit boards, mobile phones with broken screens, green knobbly pieces of tempered glass from a car break-in down the street. Everything is arranged in linear order on a shelf above his bed.

In any other child I’d wonder if his obsessive neatness was a symptom of some spectrum disorder, but Peter has weaponised his tidiness: he knows how disturbing his father and I find it.

I turn from the window overlooking our street and see Peter standing in the doorway, watching me.

‘Did you find what you were looking for?’ he asks.

‘I wasn’t looking for anything,’ I say.

‘Then why were you in here?’

‘Just getting a feel for you,’ I say evenly.

This seems to satisfy him. He sits down on his bed like a four-year-old on his first day at primary school, criss-cross applesauce. He’s still in his school uniform, which makes him look even younger than his years.

‘Do the police think you murdered Felix?’ he asks conversationally.

I’m too taken aback to correct him: Mr Porter to you. ‘Why would you think that?’ I ask, recovering quickly.

‘They took away your running shoes because they had blood on them,’ Peter says. ‘They must think you killed him. Did you?’

‘Of course not,’ I say, matching his casual tone. ‘How do you know about the police?’

‘I heard you and Dad talking about it last night.’

It was almost midnight when Tom and I slipped out into the back garden so we could talk where neither of the kids could overhear us: sound carries in our house, and the walls are thin. Peter must have followed us and hidden in the shadows: he’s light and stealthy on his feet, like a cat. We’d never have heard him.

I try to remember what else we discussed last night. We talked about Peter, I know that. Tom was angry I let him spend the day at the studio with Stacey on Monday.

So much for punishing him for trying to drown a kid! We can’t keep ignoring this, Millie, and hoping it goes away.

You’re the one who’s had your head in the sand for ten years.

Well, I’m wide awake now.

So what is it you suggest we do?

I don’t know. But we can’t carry on as we are. We need to—

We need to what, Tom?

‘What were you doing up so late?’ I ask my son, as if that’s all that matters.