spend the rest of Saturday evening and Sunday morning preparing for my visitor and trying to coach my sister on the pitfalls of modelling. Tabby’s been animated and glowing ever since we returned from London, and her total lack of poker-face has not gone unnoticed.

“I don’t know what you two did together yesterday, darling,” Bunty says warmly as I walk into the kitchen, “but Squirrel has been beaming like the moon all morning.”

My sister squeaks and waves at me conspiratorially from her highchair. If we’re going to start lying to our family regularly together, she’s really going to have to work on her facial expressions.

She has no idea how to play it cool.

“Oh really?” I say vaguely, giving Tabby a firm chill out look. “Science has shown that children with siblings four or more years older tend to be much smarter and have fewer allergies compared to those without. I think maybe she’s just happy to spend more time around me.”

“I don’t doubt it, darling,” Bunty smiles.

Then I start rooting energetically through the cupboards. “Do you know if we happen to have any Steak and Ale Pie lying around? Or maybe some Haggis?”

“Haggis?” Annabel enters the kitchen with Dad two inches behind her. “Harriet, why on earth do you want minced sheep’s organs at 9am on a Sunday morning?”

OK: eww. I thought it was some kind of Scottish dessert. “Fish and Chips? Toad in the Hole? Bubble and Squeak?”

“I have a sausage roll,” Dad offers, pulling a greasy paper bag out of his pocket. “And some Haribo eggs.” Four emerge, stuck together. “And a liquorice lace. Maybe a few cheese crisps.”

We all stare at him.

“What?” he says defensively. “It was a long train journey from Manchester and I got hungry.”

Apparently the nematode worm has a brain shaped like a doughnut.

Sometimes I wonder if my dad does too.

“Still doesn’t explain why they’re in your dressing-gown pocket, Richard.” Then Annabel bends down and gives Bunty a gentle kiss. “Good morning, Mum.”

Annabel’s eyes are puffy and her face is kind of splotchy. Honestly, she looks more exhausted than she did yesterday.

They should ask that spa for their money back.

“Good morning, my angel.” Bunty smiles again and points at the wall. “Look, Bells. A rainbow. Do you know what that means?”

Annabel turns to the kitchen sink.

“Refraction,” I answer for her, pulling out a tin of mushy peas. “It means white light is passing through that crystal and separating it into different wavelengths that we perceive as colours.”

Then I pile a tin of mushy peas, some Cadbury chocolate, a packet of Jaffa Cakes and three packs of Walkers Crisps into a basket and glance at my watch.

Yup: I’ve timed it perfectly.

“Harriet?” Annabel says, turning round as I grab the basket, my satchel and three full carrier bags and start hefting them towards the door. “Where are you going now?”

I pause in disbelief.

“I literally told you,” I say in frustration, plonking my bags back down. “Four times. Not including that.”

I point at a laminated sheet, stuck to the wall:

Underneath this message is a colour-coordinated chart for the whole family. I’ve highlighted it in bright yellow pen and stuck a note next to it that says

with hot pink arrows.

I’m not sure what else I could have done.

“I remembered,” Dad says smoothly, putting his arm around my stepmother as she blinks at the message. “And I’ve bought a spare air bed. You just get back to turning the hot tap off, sweetheart, before you drown us.”

Water’s beginning to spray all over the kitchen.

On second thoughts, maybe I don’t need to worry. It feels like I could turn Tabitha into a purple Chihuahua at the moment and Annabel wouldn’t notice.

“Thanks, Dad,” I say gratefully, kissing his cheek. Then I add in a whisper: “You might want to look into changing Annabel’s antihistamine meds.”

Dad smiles. “It’s on the list.”

And – for the second time this week – I pick my bags up and start heading back into London.