But when they take her from the room, she looks back at us, and the expression on her face is so clouded, so unrecognizable, that I think to myself: She’s a stranger already. My own child. No one I know.

Eventually, Trevor drives us home. I don’t know where my car is – at the school, perhaps. God knows if I’ll be able to go back there to retrieve it. How I’ll ever be able to show my face again. What I want now is to curl up in a hole so deep no one will ever find me.

I look out at the blackness of night, all the houses, the neat gardens, windows lit up against the dark. Box hedging, plantation shutters, SUVs in the driveway. Basketball hoops bolted to garage walls, trampolines on the lawn. Everything neat and safe and tucked up, secure. This slice of suburban life. Tennis clubs and swim teams. We thought we were insulated. All these things we have, everything we’ve accumulated, thinking it could protect us. But the enemy was here all along, living among us, making itself comfortable in our house.

And I think now of all those other parents out there. I think of Craig and Irene Ferguson – shocked, appalled, furious at their son for involving them in this way. They will have charges to answer too, about the gun, how it came into Beth’s hands. But tonight, I know their anger will give way to relief. A prayer offered up in thanks. Their boy is alive. Safe within their home. He survived. He was spared.

And Siobhan Harte. In her mock-Tudor mansion with its tennis court, its home cinema, her ear burning against the phone as she relays the dramatic sequence of events to yet another friend, the gratifying shock resounding in their response. ‘It could so easily have been Sasha. When I think about it – the two of them up there in front of the whole school, Sash and that little psychopath. She pointed the gun right at Sash, you know …’

There but for the grace of God, they will say. Holding their own children a little closer tonight.

People will look at our house and shudder. That’s the house, they’ll say – those three girls: two of them dead and one in prison. Walking on quickly as if chased by a cold wind.

‘Will you come in for a drink?’ Mark asks, as Trevor pulls into our driveway.

But the engine is still running, and Trevor has the look of a man who wants to escape, to try and expunge what he’s learned today, contaminated by the knowledge.

‘I’ll leave you two alone,’ he says, adding: ‘Be good to each other, won’t you? What you’ve gone through today is just about the worst thing any parent could go through. You’ve got to be kind to each other now.’