My God, my God. Everything has stopped, everyone is looking: parents, children. Everyone has seen. I thrust my crumpled paper plate into Sally’s hand. My voice sounds disembodied as I say, ‘I’m sorry, excuse me, please take this.’ My ears have gone dead, like I’m underwater – or like Charlie’s roar has burst my eardrum. I feel stripped naked, completely exposed.

I push through the crowd and grab my son by the arm, my sticky hand creasing and smearing his clean shirt. I drag him clear of the circle of chairs and children and elbows, even as he fights and twists in my grasp. I can see Molly’s mum stepping forwards, concern written all across her face. But all I can focus on is getting us out of there, getting him out of there.

It feels like sports day all over again, but this time the voice in my head is pounding, It’s real, it’s real, it’s real. It isn’t your anxiety, your paranoia, your crazy brain, because you weren’t anxious, you were happy when you saw it, heard it. Happy and calm and clear in your mind and it still happened. His rage, his eyes, his stutter; you can’t keep pretending. Something’s wrong in him, you know it is, you’ve just been ignoring it while you obsessed about Sarah. But this is happening, you’ve been right all these months, and so you need to get him out of here right now.

I don’t stop to say goodbye to anyone. I don’t even thank Molly or her parents for the balloons or the games or the cake. I drag Charlie down the hallway, wrestle him into his coat and shoes. He pretends he has no idea what is happening. ‘Are we leaving, Mum? Are we going?’

‘Yes,’ I tell him, already swiping for a taxi on my phone. ‘Yes, we’re leaving right now.’

‘No!’ he cries. ‘No!’

I just manage to get him outside, into the cold and away from the house before he bursts into tears.

As soon as we get home, I strip Charlie out of his party clothes and put him into his pyjamas. I get the thermometer from the cupboard in the kitchen and push it under his tongue. When I pull it out, I read the gauge without showing him.

‘You aren’t very well,’ I tell him. ‘You have a temperature.’