‘No, no . . . I was not one of them, but there were so many that no one in my country trusted each other during the Cold War, after they built the Wall. When the East was split from the West like I told you. My country had a secret police, a police that watched everyone, all the time. It was called . . .’

‘The Stasi,’ I whisper.

‘Yes.’ Granddad nods. ‘How did you know?’

‘Jake told me. He looked it up.’

Granddad makes an ‘mmm’ sound like he might have forgiven me but not Jake.

‘As I was saying, my country was full of spies. You could not trust your neighbour, you could not trust the owner of the corner shop, sometimes you could not trust your own family. Every shop, every office, every room could have a listening device.’

‘So it really was like in Pawn Sacrifice,’ I say. ‘When Bobby Fischer thought his room and the telephone were bugged.’

Granddad waits for the man with the girl in the pushchair to pass us.

‘Yes.’ Granddad checks his rear-view mirror. ‘It was just like that.’ His voice is so low, I can hardly hear him. ‘They had listening devices everywhere; your great-grandfather, great-grandmother and I, we could not even talk in our own home, and when we went out we would be followed. Guards stood in towers and aimed guns down onto the street. So we stayed in all the time. If we wanted to say something important we would write it down on a piece of paper and after we’d read it we tore the paper into tiny pieces so the spies would never know what we had written. And we kept our curtains closed all the time, just in case they were watching from across the street. It was always dark, but at least if we couldn’t see out, then they couldn’t see in. And of course we couldn’t escape because they had built the Berlin Wall. The Wall that split the East from the West that I told you about.’

I try to think of something to say, but Granddad’s life sounds so bad it’s like a film. I wonder if it can really all be true, but from the serious look on his face I can tell there’s no way he has made the story up.

I stare out of the window. Sometimes I feel like the square is closing in on me, that everyone knows what I’m doing, but that’s really only Mrs Flower when she snitches on me for going into her garden to get tennis balls. Mum says she knows everyone’s business. But what must it be like to have thousands of Mrs Flowers – going through your rubbish, listening to every word that you say? Even that doesn’t feel anything like as bad as what Granddad had when he was growing up. They had uniforms. They had guns.