‘Those balls are like planets, so is it the solar system?’

Casey shakes her head patiently. ‘No. It shows how proton-beam therapy works. So that’s a hydrogen atom, and you see the sparkling thing in the middle? That’s the proton, which they fire at top speed at the tumour in my head – hopefully missing my actual brain. Like a bolt of lightning that only hits the bit that needs to be destroyed?’

‘Wow.’

‘They have a thing called a cyclotron in the basement and I’m one of the first kids in the country to get treatment here. You used to have to go to Florida. Some of the kids I met in Birmingham went and were treated like VIPs. Got taken to Universal Studios and SeaWorld and everything.’

‘Maybe, when this is all over, your mum can take you.’ I remember what Casey said last night about not having a passport. ‘Or there’s a pier at Weston-super-Mare. They don’t have rollercoasters, but there are dodgems and slot machines.’

Casey is unimpressed. ‘Huh. After the rainforest restaurant disaster, I’m not wild about trying another of your recommendations.’

‘Sorry.’

She grins. ‘Joking. I love piers, but we live miles from the seaside.’

‘I’ll take you in the jeep one day.’

‘Really?’

I nod. ‘It’s a promise.’ One I can keep.

‘Shall I show you the lounge now, and my school?’

‘You have to go to school?’

She pulls a face. ‘It’s totally unfair, right? But I only do a few hours each day, because I get tired otherwise.’

I follow her into the main part of the hospital. The buzzing’s getting so loud now I can barely hear what Casey is saying to me.

I close my eyes, trying to block it out. Instead I hear someone else’s voice, one I know can’t be real:

‘Come on, kiddo. Chin up; the sooner we get you seen, the sooner we can get home. We’re missing Noel’s House Party.’

This woman sitting opposite us is knitting super-fast, even though her nose is bleeding onto the yellow wool. Dad’s tried to talk the receptionist into letting us jump the queue but, for once, the charm’s failed.

On the plastic chair we’ve lined up snacks: Hula Hoops and Toffee Crisps and Dr Pepper, because Dad knows this trick that lets you get six items from the vending machine even though you paid for one.

It’s past midnight and I doze against my dad’s shoulder and I can smell Extra Strong Mints in his jacket pocket. Dad’s biggest fear is bad breath, because you only get one chance to make a first impression.

‘Darryl Lennox?’

Everything gets scarier after they take me through. Tests and phone calls and a procession of frowning doctors. And at the end of it, the lady doctor says, ‘We’d like to keep him in overnight’, even though it’s already morning.

‘He’s not seriously ill, though, is he? Nothing a giant bar of Dairy Milk won’t fix?’ Dad says.

The lady doctor smiles, but one half of her mouth doesn’t turn up. ‘Until we diagnose the problem we can’t be sure, but we’ll have answers for you soon.’