or the next couple of days, I simply refuse to leave my room.

There’s no point. The alternative is to watch my parents take all my impeccably arranged books out of the study and pile them in a not-even-vaguely alphabetical order outside my door.

By the time it gets to Friday afternoon, I’m so sick of hearing Dad say “another book of random quotations? Seriously?” I decide to go for a long, cathartic walk. My ex-best friend will be in France by now, getting chased about by Mr Green Lycra Cycling Shorts.

Good. Serves her right.

I hope he doesn’t even use proper virgin olive oil, and opts for low-grade cooking oil instead.

Unfortunately my stress-reducing exercise efforts are ruined within two minutes by a small, fluffy-headed figure creeping from tree to tree in front of me. I have to keep looking in the opposite direction so I don’t hurt his feelings.

“Toby,” I finally say as I turn back on to my road. He flattens himself behind a lamp-post considerably thinner than he is. “I can see you.”

“Are you sure?”

“Pretty sure, yes.”

“Oh dear,” he says sadly. “My homemade camouflage stalker kit may need some more work.” He points at his grey T-shirt and grey trousers. They have faint black lines drawn on them in criss-crosses.

I stare at him, and then totally give up. “What on earth are you camouflaged as?”

“Pavement.” Toby lies down on the floor and holds himself very rigid and still. “See? It’s only for urban settings, obviously. It wouldn’t work in the countryside.”

I laugh and carefully step over him.

“Harriet,” he says, jumping up and running after me. “Are you and Natalie OK? I couldn’t help overhearing a small amount of very loud fighting the other day when I was sitting in the rhododendron outside her house waiting for you to come out.”

Clearly Toby hasn’t moved on quite as much as I thought he had. “I’ve had an unexpected best-friend position open up,” I say tensely. “Would you like it?”

“Would I?” Toby shouts, jumping up and down. “I mean, I would. Just to make that clear.”

“Great,” I say sharply. “We’re now Best Friends. We can go and get some badges made up or something.”

Toby bounces along next to me in contented silence, and then sighs. “I’m afraid I don’t think I can take the job, Harriet,” he says sadly. “You and Natalie are soulmates, except you don’t kiss. It would be wrong to try to ever separate you.”

I make an ambiguous snorting noise. Soulmates are usually happy for each other when supermodel ex-boyfriends text them. “Either way, now I’m not going to Tokyo, it’s just you and me this summer.”

“Actually, maybe not,” Toby says solemnly.

I’m already thinking about my abandoned Summer of Fun Flow Chart. Maybe I can re-use it after all. I just need to find the right colour pen so I can cross out Nat and replace it with Toby and my holiday will be none the wiser. “Hmmm?”

“I think you already have a visitor.”

My stomach suddenly flips and every hair on my body stands on end. Nick?

I look up. There’s a bright pink Beetle parked outside my house.

The hairs flatten back down again. Oh no. No no. No no no no – I turn around and start walking in the opposite direction.

“Harriet?” a voice calls. “Come and give your favourite old person a nice big cuddle.”

And there – standing in the doorway covered in bells and sequins, like some kind of summery Christmas tree – is my grandmother.

I just want to make something perfectly clear.

There are many, many other old people I prefer to this one. My grandad, for instance. Nat’s grandad. Nat’s grandma. My old piano teacher, Mr Henry. The ancient lady who works in the local newsagent and gives me free sweets without being asked.

It’s not that I don’t love my grandmother. I just don’t really know her very well.

Or at all, actually.

“Sweetie!” she says as I approach with tiny steps, the way you might a rampaging hippopotamus. “Your hair is even redder than it used to be!” She sweeps me into her arms and all the bells on her wrists tinkle like she’s an enormous cat. “From a distance it looks like your head is on fire!”

I think I’m about to get an embroidered daisy imprinted permanently on my forehead. “It’s strawberry blonde,” I tell her left breast as politely as I can. She smells of wood and beetroot.

“Look how mucky you are!” she laughs, pulling back and spitting on her long wizard-like sleeve. Before I can escape she starts scrubbing it hard on my nose. “Oops. No. They’re freckles, just like Richard’s. Adorable! How long has it been since I saw you last? Five months? Six?”

“Three and a half years,” I say, staring over her shoulder at my parents who have finally emerged. Needless to say, Annabel’s eating. This time it appears to be toast with Neapolitan ice cream spread in a layer on top.

“Whoopsy,” my grandmother says, beaming at us. “I took over a coconut stall in India for an afternoon and next thing I knew I was running a roaring backpacker trade. Good for copious amounts of diarrhoea, coconut water.”

Toby races forwards with his hand out. “I am Toby Pilgrim, Harriet’s stalker. Nice to meet you, Mrs Grandmother Manners.”

“Bunty,” she says cheerfully, shaking it.

“And on that exciting note,” Toby says, wiping his nose on his finger, “I shall make my dramatic exit. I’ve got this new plate with a face on it and Mum’s made spaghetti so I’m eager to get home while it’s still hot and malleable enough to form realistic hair.”

Then Toby promptly waves and scoots back out of the door. We all try to pretend that we can’t see him immediately crouch down behind the hedge right outside.

“I didn’t know you were coming.” I look at my parents with round eyes. Does nobody tell me anything these days?

“Well, if somebody needs to take you abroad it might as well be somebody who spends most of her time there, right?”

I stare at her, then I stare at my parents, and then I stare at my grandmother again. What?

“Apparently Tokyo is the place to be this summer,” she grins. “I think we should check it out, don’t you?”

I suddenly don’t care that I’ve probably met my nomadic grandmother a handful of times in my entire life. I don’t care that her hair is sort of baby pink, and I don’t care that she currently has what looks like a twig stuck in it.

I don’t even care that the last time I saw her we had a forty-five-minute conversation about the benefits of wiping your bottom with your hand instead of a piece of toilet paper to ‘save the rainforest’.

“Oh my God, I love you!” I yell, throwing myself around her neck. “Thank you! Thank you thank you thank you!”

“Now, that’s the greeting I was looking for.”

Then I lob myself at Dad, and then – a little bit more carefully, in case I squish my sibling – at Annabel. “Thank you! Thank you thank you! You’ve saved my summer! Totally saved it!”

Dad laughs. “How could we argue with a Powerpoint presentation of such quality, Harriet? We’re not monsters.” He puts his hand over his mouth. “She’s a monster,” he pretends to whisper, pointing at Annabel. “But I’m not.”

“Go upstairs and get your things packed for tomorrow, Harriet,” Annabel says calmly, ignoring Dad. “I imagine your grandmother will want to help you write a brand-new Summer of Fun Flow Chart.”

“What’s a flow chart?” my grandmother asks. “Does it rank rivers?”

Good Lord. I’m going to have to start training her immediately. “We have new plans to make!” I shout, running up the stairs. “Itineraries! Schedules! Lists! Lists and lists and lists and—”

“Look, Harriet,” my grandmother says as she follows behind me, pointing at the garden. “A squirrel!”

“Make sure she has everything she needs,” Annabel calls after us.

“My darling daughter,” Bunty calls down the stairs. “That’s the beauty of foreign travel. You don’t need anything but yourself.”

“And a passport, Mum,” I hear Annabel say tiredly. “And tickets. And a visa. And clean clothes and quite a few changes of underwear.”

Uh-huh.

If you thought you saw a marked family resemblance between my maverick grandmother and my maverick father, you would be wrong.

Bunty isn’t Dad’s mum.

She’s Annabel’s.