By Wednesday afternoon, though, I am wrung out. Charlie is already fractious when we get back after school. I haven’t been near the supermarket and we have run out of all the things he likes for dinner. The only option is cheese on toast, but he hates cheese, he tells me, which isn’t even true, but he is in a bad temper. I stand at the grill and pull out the toast, which I have managed to burn at the edges. More than ever now, despite my efforts, I can’t get Sarah out of my head. I feel the questions crawling round my skull, like insects. I can’t stop going over everything Marianne said, all the other fragments I’ve collected about Sarah. Every tiny thing I remember about her. Sometimes the pieces look as though they might come together but a moment later they all unravel, nothing to hold them in place; then the whole process starts all over again.

I set the grill tray down and take a deep breath, forcing the branches of my lungs to open. I have to focus, I have to set my questions aside, lock them up at the side of my mind. I give Charlie ketchup and his favourite drink and it’s enough, this time, for him to accept the sorry dinner I’ve made.

After he’s finished eating and I’ve washed up his plate and cutlery, we sit together on the living-room sofa, so I can help him with his maths homework. He has a book of arithmetic to work through, two pages of sums and subtractions.

Charlie is okay at maths usually, but this evening he is rushing the questions, making silly mistakes on problems I know he can easily solve. Can’t he?

I watch him hesitating over the numbers, not seeing the obvious solutions.

‘What’s wrong?’ I finally blurt out. ‘You know you can do these.’

But what if he can’t? What if something has changed, slipped within him? Could it happen like this? I try to think about what I have read online, but all the information has tangled up in my head. I can’t seem to sort it out.

Now Charlie is getting angry, emotions bubbling up within him, and my heart cries that the fact he isn’t controlling his temper is another sign.

I pull the workbook out from under his hands, his pencil scratching a streak across the page. I set it on my own lap and flip back through the pages, right back to the beginning, to the problems I know he could practically do in his sleep.

I set the book back down on his knees, pushing the pages back under his fingers. ‘Here. Show me.’

He looks up at me, a mixture of anger and anxiety twisting his features. He knows it’s a test.

‘These ones,’ I say. ‘Show me. I need to see that you can do it.’