At home it turns out I’ve got even more to worry about than Curtis. When I come into the kitchen, Mum and Dad are arguing and there’s a line between Mum’s eyebrows. I know that line – her stress levels are about to go from a banging-cupboard-door seven to full-on-furious ten.

‘Zelia, you’re putting yourself in too much danger!’ Dad sounds cross but I think he’s actually frightened.

My stomach impersonates a yo-yo. What has Mum been doing and just how much trouble is she in? ‘What’s going on?’ I ask.

Mum lets out her breath in a long whoosh. ‘I had a bit of a narrow escape because someone was on my tail. I needed to lose them before getting into my new spy-gadget supplier disguise but I had trouble shaking them off even in the car. I came close to missing my meeting with the double agent to give him the first gadget you picked up – and that would have been a disaster. It looks like someone out there is watching me and that’s not good.’

If Mum had trouble shaking an enemy off in the car then it’s got to be serious – my mum is the fastest driver in the known world!

‘You have to agree to it now,’ Dad says softly.

Mum and Dad exchange looks and then Mum sighs a hurricane-force sigh. ‘I know,’ she says. ‘But I still don’t like it.’ Her shoulders slump. All the anger’s gone out of her. ‘I’m sorry,’ she tells me. ‘I really am. But I’m afraid difficult covers sometimes go with the job of being a spy.’

It feels like someone’s sliding an ice cube over my skin. I know what’s coming.

I keep staring at Mum, willing her to tell Dad to forget it again. But her forehead’s still all creased up. Which means … trouble.

‘I can’t,’ I say.

‘It’s not like you’d have to do it for long periods,’ Dad says. ‘You’d only have to be in the disguise for about an hour at a time.’

Grown-ups are always doing that – trying to make you feel stupid for objecting to something because it’s ‘not for long’. They don’t seem to understand that if something is embarrassing, the laws of time change and every second feels like an hour and every minute feels like ten years and every hour feels like forever.

‘No,’ I say.

Dad looks at me, his eyes all flinty. ‘We need to make sure your mum’s safe.’

It’s weird when Dad gets stern. He looks all wrong – like a teddy bear pretending to be a shark.

‘Josie, I wouldn’t ask if I didn’t have to,’ Mum tells me. ‘But this mission is even more dangerous than we first thought. If you can cover for me at home, it will help protect me.’ The line between her eyes is now deep enough to plant a row of seeds in. She must be really worried. Suddenly I feel like I have to look after her instead of the other way around.

I take a deep breath.

‘It doesn’t look like I have much of a choice then, does it?’ I say.

Mum hugs me. ‘Thank you,’ she whispers. ‘And I really am sorry.’

‘I know,’ I tell her. ‘It’s okay.’

At least Mum knows what she’s asking. Dad doesn’t have a clue. Now that I’ve given in he’s acting as if we’re all on our way to a funfair.

‘Good, good, good,’ he says cheerfully. ‘Don’t worry, it won’t be very different from pretending to be Josie.’

It won’t be very different? It won’t be VERY DIFFERENT?! Pretending to be a girl my own age is a piece of easy-bake cake compared to dressing up as my own mum. I thought wearing tights and a dress was horrendous, I thought wearing a tutu was appalling, but wearing a padded bra and high heels? What is wrong with him?

I swear to myself that when I am a real, grown-up spy, I will take revenge on him for all he’s put me through. I’ll make sure I get promoted so I can be Dad’s boss and then make him dress up as an orang-utan for a mission in London Zoo. He can eat bananas and pick fleas out of his ears for a week or two. Let’s see how easy he thinks disguises are then.

‘Right, well, you’ll need to do your first mission as Mum in two days,’ Dad says, unaware of my future plans for him. ‘So be home straight after school tomorrow for training.’

‘Two days? I can’t learn how to walk in heels in two days!’ I stare at Dad. He has got to be kidding.

‘Sure you can,’ Dad says. ‘It’ll be as easy as falling off a log.’

Falling is exactly what I’m worried about.