Next day, the head admits that I’ve worked harder this year than in the previous six years put together, and Mum says yes, I can go. I tell Edie the news about my trip.

‘Really?’ she says. ‘Are you sure? I think I can manage on my own.’

‘Don’t worry, it’s sorted,’ I tell her. As opposed to ‘No you can’t – you’d be a walking disaster area,’ which is what I’m thinking.

Liam is thrilled for me, and really jealous. He’s always wanted to go. We spend long evenings on Instant Messenger, saying how much we’re going to miss each other, which in my case is totally true, but there’s something else that I’m not admitting to.

I’m quite relieved that there will be a few days at least when he can’t pester me about talking to Mum. I know he thinks it’s a great idea for us to have a heart to heart about Vicente, but frankly, I’d rather do that Shakespeare mock ten times over. And it wasn’t fun the first time, believe me.

‘If you tell me ONE MORE TIME how much nicer it is in First Class, I will personally attack you with this plastic spoon,’ Edie says about halfway through the flight. I realise I might have mentioned the big seats a few times, and the legroom, the clothes, the magazines and movies, and the celebrities . . .

Edie is deep in one of her four guidebooks, and making notes.

‘I’ve got it down to twelve major sights that we can’t afford to miss,’ she says. ‘If we start with Ground Zero at the south end of Manhattan Island and work our way systematically north towards Central Park, we should be OK.’

‘This is a trip to see Jenny,’ I point out. ‘Not an expedition to the North Pole.’

‘Yes, I know,’ Edie says irritably. ‘But while we’re there . . . I mean, imagine not seeing the Guggenheim, or the Met, or the Public Library. Oh, goodness. I’ve left out the Statue of Liberty.’

She goes back to her notes and starts scribbling again.

Frankly, the Public Library, lovely though I’m sure it is, would not make my top twelve sights. Not since I’d have to fit in Saks Fifth Avenue, Barneys, Bergdorf Goodman, Bloomingdales, Tiffany and all the little shops in the back streets of SoHo. And the Frick, whatever that is. But I don’t have a list. I’m more a ‘take it as it comes’ sort of a girl.

Also, I have better things to do with the rest of this flight than make lists. Liam gave me a longer than usual goodbye kiss yesterday, to last me until I get back to England. I close my eyes and try to remember it. Turns out, this is even more fun than sitting in First Class.

We land in the evening. A bright yellow taxi whisks us down freeways and through tunnels until suddenly we’re in the high-rise corridors of Manhattan by night. To start off with, Edie tries to chat to the taxi driver and ask for his advice on places to see, but we eventually realise that he’s not talking to us, he’s talking into a headpiece attached to his phone, and he’s speaking a language we don’t even recognise. Edie gives up on the tourist advice and makes do with staring out of the window at the lights.

We reach a wide, low-rise road, where the trees are hung with fairy lights. West Broadway, in the heart of SoHo. I’m thinking it can’t get any more magical, when the driver pulls up.

‘Here,’ he says gruffly. He points at the meter and I start scrabbling around for dollars. I’m the one in charge of money on this trip. While I’m counting, he extracts our bags from his boot and the second I’ve paid him, he’s gone.

‘Huh! Not exactly an advert for his city,’ Edie says to his departing tail-lights.

But I don’t care. I can’t help grinning. I’m in New York. It’s freezing cold and so far we’ve only heard one word in English, but this street is beautiful. The lights all around us are twinkling their welcome. We’re about to hang out with a supermodel during Fashion Week. So far, so extremely good.

Isabelle has spent the whole day doing shows and interviews. She’s been up for sixteen hours. She opens the door wearing no makeup and looking like a Botticelli angel.

‘I’m sorry I’m not going to be here much,’ she says, showing us around. The apartment has two small bedrooms and an open-plan kitchen and living room overlooking the street. It’s furnished with a mixture of antique textiles and junk shop finds and I love every centimetre of it.

‘I’d show you the city, but I’m only here until tomorrow night, then I’m off to London,’ she says. ‘I’ll have to leave you to it, but I’ll tell you where to go, if you like.’

‘That would be great!’ Edie says. She may have several pages of notes on exactly what to do in New York, but she’s gradually returning to her old self, and her old self can never have too much information.

‘First, though, you must be starving,’ Isabelle says. ‘I always am when I get in. What would you like? I recommend the Thai curry. Or the dim sum.’

She rummages through the drawer of a mirrored console table and throws us a menu. It’s several pages long, covering every world cuisine I can think of. And several others that I suspect have been made up by New York chefs, just to be different.

She’s right about us being starving, but wrong about us feeling adventurous. We settle for burgers and chips. Later, while we’re making a small dent in the largest portions of food I’ve ever encountered – apart from in Chicago – she tucks her long legs under her and asks us about London.

‘How’s your mum, Nonie? And your granny?’

I try not to wince and tell her they’re fine.

‘And Harry? He had a cold the last time I saw him. That was eleven days ago. Did he manage to get rid of it? He looked so tired and grizzled, poor thing. I gave him every vitamin I could think of, but I’m not sure he took them.’

‘He’s fine too,’ I assure her. ‘He sends you lots of love.’

Actually, I’m making this bit up. It’s just occurred to me that he probably should have sent her lots of love, but he was so busy telling me about his favourite old record stores in the area that he forgot.

Nevertheless, I’m a good white liar, and Isabelle glows with pleasure.

‘Well, I’m seeing him in three days anyway, so I can check up on him then. And make sure he takes those vitamins.’

I look around her living room. Harry is everywhere, in subtle ways. There are framed album covers by his favourite old bands. A road bike that surely must be his, hung on the wall just inside the door. A photo of Isabelle in the shirt she wore to their engagement party that I’m certain he took. I recognise his style. She’s even wearing one of his old tee-shirts now, I realise.

As she sits back and chats to us, occasionally running her fingers through her world-famous ringlets, I’m surprised that Harry doesn’t talk about her more often. Perhaps you just get used to it after a while – living with that much beauty. But hard as I try, I really can’t persuade myself that she’s using him just so she can have a big wedding. She seems so genuinely in love. It’s a relief, I suppose. Good to think that Harry will be happy. Except something’s still wrong. But I am far too tired and full of chips and burger to work out what it is.