‘Jake,’ I say. ‘This is stupid. He’s only come out to buy flowers.’

‘Yeah, but that’s what spies do. It’s like a secret code so they know who each other are – some wear hats or carry newspapers, or . . .’

‘Flowers.’

‘Exactly.’

Granddad comes out of the shop carrying a bunch of pink flowers.

‘And they can hide stuff in there too, like tiny cameras in the petals, and even poison in the stems.’

‘Jake. You’re making it up.’

‘I’m not! There was a Russian man who got poisoned by the tip of an umbrella. I found it on the internet when I was looking up stuff about your granddad . . . Anyway, he’s getting away from us. Come on.’

Granddad crosses the road by the kebab shop. Me and Jake sneak past the newsagent and the florist until Jake suddenly stops and holds up his hand. Granddad is talking to a man outside the chip shop – one of his friends from the GFG. They walk together. Me and Jake track them to the bus stop and crouch down behind a car.

‘Jake,’ I say. ‘This is pointless; they’re just talking like everyone does.’

‘That’s what spies do,’ Jake whispers urgently. ‘They look like everyone else so they blend in.’

Me and Jake move onto the pavement as a bus hisses by. The man gets on but Granddad doesn’t, he just glances back down the road towards me and Jake.

We jump into the estate agent’s doorway.

‘Do you think he saw us?’ asks Jake.

‘I don’t think so,’ I reply. ‘He can’t see us in our tree and it’s about the same distance.’

‘Cool.’

Me and Jake poke our heads around the doorway. Granddad is walking away from us and he’s waving at his friend on the bus as it passes him by. Then he turns down the road that leads to the park. Granddad hasn’t been to the park for ages. We used to go all the time when I was little. He’d carry my bike and Grandma would come too and I’d cycle around the botanical gardens. But why’s he going there now?

We run down the pavement and into the park until the path forks. We look left and right but all I can see is a man jogging and a woman bending down and talking to her child in a pushchair. Jake holds his arms out wide.

‘Where did he go?’

I shrug.

‘See, Felix,’ says Jake. ‘I told you that spies can vanish into thin air.’

We both spin around but I can’t see Granddad anywhere.

‘We can’t have lost him,’ I say. ‘He can’t run quicker than us when he’s seventy-two. Maybe we should just go home.’