Maggie appears just as we’re putting the finishing touches to our flour tower. ‘That’s big,’ she says, eyeing the enormous floury mountain.

Grandad adds a final spoonful. ‘It’s ten-bags-of-flour big! We’re going to drop a watermelon on it. Poof!’ His hands mime an explosion. ‘We’re recreating the impact of comets striking the moon.’

‘We’re dropping a pea on it too,’ I add. I don’t want Maggie thinking we’re about to trash her tent.

‘Sounds intriguing,’ she says. ‘I’ll be watching the second half.’ And this is when Elsa decides to pop her head up over the side of the box and scream, ‘Da, da!’

Maggie jumps back, a horrified look on her face. ‘It’s a baby!’

‘My other granddaughter,’ says Grandad. ‘We’re dropping her in the flour as well!’

Maggie laughs weakly and Grandad must realise she needs to be reassured because he adds, ‘You don’t need to worry about Elsa getting in the way. Pete will look after her during the show.’

Somehow I doubt that. In the car Pete tried to give Elsa his Homer Simpson lighter to play with and when we arrived he offered her a king size Mars bar. I don’t think he’s had much experience with babies.

Maggie frowns down at Elsa, then her eyes flick to me. ‘Well, just as long as you’ll be supervising both your granddaughters the whole time. Meg’s not old enough to do this on her own yet.’

‘I won’t let either of them out of my sight!’ Grandad promises.

Just then, Maggie’s walkie-talkie buzzes and she backs out of the tent. ‘Make sure you don’t.’

The moment she’s gone, Grandad turns to me. ‘You watch Elsa. I’m going to buy a sausage roll.’

TWENTY-FOUR

‘You’re one hundred per cent sure about this?’ I’m wearing a lab coat, a curly grey wig and black specs. I’m a mad scientist. Grandad’s wearing something similar, only he doesn’t need the wig.

‘Definitely,’ he says. ‘Kids love costumes. Now hold still while I do your make-up.’

He dabs black face paint all over my face. It’s supposed to look like something’s exploded. Grandad’s already done his and it does look quite good, especially with his back-combed hair. ‘You’re so pale it looks extra effective!’ he says, putting a final smudge on my forehead.

I’m pale with fear: there’s a constant rumble of voices coming from outside the flaps of the tent and every now and then a curious face peeks in.

Pete wanders by. ‘It’s mad out there. I’m going to have to let them in. Are you ready?’

‘Born ready!’ says Grandad, and I swallow and think, Stay down Shreddies, stay down!

Pete holds back the flap and children start to pour in, shrieking and pushing each other as they race for the positions at the front. They’re followed by their parents – real, live grown-ups. I hadn’t really thought about them … They’re so big!

‘Look at the clown, Mummy!’ shouts a boy, pointing at me. ‘He’s scary!’

‘It’s a lady clown,’ says his mum, giving me a smile.