I sit on the sofa with my head in my hands. I imagine him putting on his long coat, listening for the clink as he picks up his car keys and the click of the latch on the front door.

But there’s no sound, just the clocks tick-tick-ticking from everywhere like they are built into the walls. Is this what spies do? Just disappear without even saying goodbye?

A shadow creeps across the doorway. I lift my head slowly. See Granddad’s worn slippers, then his brown trousers, and his blue jumper that Grandma knitted for him. And tucked under his arm is the box file I saw in his wardrobe.

He smiles as he steps towards me.

‘You remember I said we should trust each other?’ he says softly.

‘By the tree, Granddad?’

‘Yes.’ He sits down beside me and puts the box file on the coffee table. ‘Well, I am thinking, I should trust you now.’

Granddad opens the lid slowly.

‘This . . .’ he says. ‘This is something I have only told one person, and that was your grandma.’

‘Not even Dad?’ I ask.

‘No, not even your father.’ Granddad sighs as he looks into the box. ‘Felix, this box contains a sad story, one that I don’t like to think of, but . . . but . . . Perhaps I should just show you what this box is.’

I stare down at the box. There are hundreds of questions in my head, but it doesn’t feel right to ask one now.

Granddad reaches in and pulls out the black and white picture. He holds it in front of me between his fingers. I hold the other side to stop it from shaking.

‘This picture was the last that was taken with my father. It is also the last chess tournament I ever played. I was seventeen and it was taken after I won the German Youth Chess Championship in 1960. Like Bobby Fischer, I was the youngest chess champion of my country and everyone thought I would challenge for the World Championship like he had. I loved playing chess, it was my passion – pitting my mind against other players was the best feeling in the world. I used to play on my own in my room all the time, all day and night, but it ended up with me not being able to see my father again.’

‘How, Granddad?’ I turn and see tears welling in Granddad’s eyes.

‘Do you remember what I told you about the Berlin Wall, how they built it overnight in Berlin, my city, to split the people in the East from the West?’

‘Yes, Granddad,’ I say. ‘They built it the day you tried to go and see your sister.’