'Luggage,' he says, and hands a tenner to the driver. 'Keep the change.'

Luggage! Suitcases and holdalls and stuff like that. As I wander round the department, looking at Louis Vuitton suitcases and calfskin bags, I'm quite thrown. Quite shocked by myself. Luggage. Why on earth have I never considered luggage before?

I should explain. For years now, I've kind of operated under an informal shopping cycle. A bit like a farmer's crop rotation system. Except, instead of wheat-maize-barley-fallow, mine pretty much goes clothes-makeup-shoes-clothes. (I don't usually bother with fallow.) Shopping is actually very similar to farming a field. You can't keep buying the same thing – you have to have a bit of variety. Otherwise you get bored and stop enjoying yourself.

And I thought I had as much variety in my shopping life as anybody. I thought I had all the areas covered. To be honest, I was quite blas about it. But look what I've been missing out on, all this time. Look what I've been denying myself. I feel quite shaky as I realize the opportunities I've just been throwing away over the years. Suitcases, weekend bags, monogrammed hat boxes… With weak legs, I wander into a corner and sit down on a carpeted pedestal, next to a red leather vanity case.

How can I have overlooked luggage for so long? How can I have just blithely led my life, ignoring an entire retail sector?

'So – what do you think?' says Luke, coming up to me. 'Anything worth buying?'

And now, of course, I feel like a fraud. Why couldn't he have wanted to buy a really good white shirt, or a cashmere scarf? Or even handcream? I would have been able to advise him authoritatively and even quote prices. But luggage. I'm a beginner at luggage.

'Well,' I say, playing for time. 'It depends. They all look great.'

'They do, don't they?' He follows my gaze around the department. 'But which one would you choose? If you had to buy one of these suitcases, which one would it be?'

It's no good. I can't bluff.

'To be honest,' I say, 'this isn't really my field.'

'What isn't?' he says, sounding incredulous. 'Shopping?'

'Luggage,' I explain. 'It's not an area I've put a lot of time into. I should have done, I know, but…'

'Well… never mind,' says Luke, his mouth twisting into a smile. 'As a non-expert. Which one would you choose?'

Well, that's different.

'Hmm,' I say, and get to my feet in a businesslike manner. 'Well, let's have a closer look.'

God, we have fun. We line up eight suitcases in a row, and give them marks for looks, heaviness, quality of lining, number of interior pockets and efficiency of. wheels. (I test this by striding the length of the department, pulling the case behind me. By this time, the assistant has just given up and left us to it.) Then we look to see if they have a matching holdall and give that marks, too.

The prices don't seem to matter to Luke. Which is a bloody good thing, because they're absolutely astronomical – and at first sight, so scary they make me want to run away. But it's amazing how quickly ?1,000 can start to seem like a very reasonable sum for a suitcase – especially since the Louis Vuitton monogrammed trunk costs about ten times as much. In fact, after a while I find myself thinking quite seriously that I too should really invest in a quality suitcase, instead of my battered old canvas bag.

But today is Luke's shopping trip, not mine. And strangely enough, it's almost more fun choosing for someone else than for yourself. In the end, we narrow it down to a dark green leather case, which has wonderful trundly wheels, or the palest beige calfskin case, which is a bit heavier, but has a stunning silk lining and is basically so beautiful I can't stop staring at it. It has a matching holdall and vanity case – and they're just as beautiful. God, if it were me, I'd…

But then, it's not up to me, is it? It's Luke who's buying the case. He's the one who's got to choose. We sit down on the floor, side by side, and look at them. 'The green one would be more practical,' says Luke eventually.

'Mmm,' I say noncommittally. 'I suppose it would.'

'It's lighter – and the wheels are better.'

'Mmm.'

'And that pale calfskin would probably scuff in a matter of minutes. Green's a more sensible colour.'

'Mmm,' I say, trying to sound as though I agree with him.

He gives me a quizzical look and says, 'Right. Well, I think we've made our choice, don't you?' And, still sitting on the floor, he calls over the assistant.

'Yes sir?' says the assistant, and Luke nods at him.

'I'd like to buy one of these pale beige suitcases, please.'

'Oh!' I say, and I can't stop a smile of delight spreading over my face. 'You're getting the one I liked best!'

'Rule of life,' says Luke, getting to his feet and brushing down his trousers. 'If you bother to ask someone's advice, then bother to listen to it.'

'But I didn't say which one…'

'You didn't have to,' says Luke, reaching out a hand to pull me to my feet. 'Your "Mmms" gave it all away.'

His hand is surprisingly strong round mine, and as he pulls me up, I feel a slight swooping in my stomach. He smells nice, too. Some expensive aftershave which I don't recognize. For a moment, neither of us says anything.

'Right,' says Luke at last. 'Well, I'd better pay for it, I suppose.'

'Yes,' I say, feeling ridiculously nervous. 'Yes, I suppose you had.'

He walks off to the checkout and starts talking to the assistant, and I perch next to a display of leather suit carriers, suddenly feeling a bit awkward. I mean, the shopping's over now. What happens next?

Well, we'll just say goodbye politely, won't we? Luke'll probably have to get back to the office. He can't hang around shopping all day. And if he asks me what I'm doing next, I tell myself, I really will say I'm busy. I'll pretend I've got some important meeting arranged or something.

'All sorted out,' he says, coming back. 'Rebecca, I'm incredibly grateful to you for your help.'

'Great!' I say brightly. 'Well, I must be on…'

'So I was wondering,' says Luke, before I can continue. 'Would you like some lunch?'

This is just turning into my perfect day. Shopping at Harrods – and lunch at Harvey Nichols. I mean, what could be better than that? We go straight up to the fifth floor restaurant, and Luke orders a bottle of chilled white wine, and raises his glass in a toast.

'To luggage,' he says, and smiles.

'Luggage,' I reply happily, and take a sip. It's just about the most delicious wine I've ever tasted. Luke picks up his menu and starts to read it, and I pick mine up too – but to be honest, I'm not reading a word. I'm just sitting in a happy glow, like the Ready Brek kid.

I'm looking around with relish at all the smart women coming in to have lunch here, and making notes of their outfits and wondering where that girl over there got her pink boots from. And now, for some reason, I'm thinking about that nice card Luke sent me. And I'm wondering whether it was just being friendly – or… or whether it was something else.

At this thought, my stomach flips so hard I almost feel sick, and very quickly I take another sip of wine. Well, a gulp, really. Then I put down my glass, count to five arid say casually,

'Thanks for your card, by the way.'

'What?' he says, looking up. 'Oh, you're welcome.'

He reaches for his glass and takes a sip of wine. 'It was nice to bump into you, that night.'

'It's a great place,' I say. 'Great for table hopping.'

As soon as I've said this, I feel myself blush. But Luke just smiles, and says, 'Indeed.' Then he puts down his glass and says, 'Do you know what you want?'

'Ahm…' I say, glancing hurriedly at the menu. 'I think I'll just have… erm… fishcakes. And rocket salad.'

Damn, I've just spotted squid. I should have had that. Oh well, too late now.

'Good choice,' says Luke, smiling at me. 'And thanks again for coming along today. It's always good to have a second opinion.'

'No problem,' I say lightly, and take a sip of wine. 'Hope you enjoy the case.'

'Oh, it's not for me,' he says after a pause. 'It's for Sacha.'

'Oh right,' I say pleasantly. 'Who's Sacha? Your sister?'

'My girlfriend,' says Luke, and turns away to beckon to a waiter.

And I stare at him, unable to move.

His girlfriend. I've been helping him choose a suitcase for his girlfriend.

Suddenly I don't feel hungry any more. I don't want fishcakes and rocket salad. I don't even want to be here. My happy Ready Brek glow is fading away, and underneath I feel chilly and rather stupid. Luke Brandon's got a girlfriend. Of course he has. Some beautiful smart girl, called Sacha, who has manicured nails and travels everywhere, with expensive cases. I'm a fool, aren't I? I should have known there'd be a Sacha somewhere on the scene. I mean, it's obvious.

Except… Except it's not that obvious. In fact, it's not obvious at all. Luke hasn't mentioned his girlfriend all morning. Why hasn't he? Why didn't he just say the suitcase was for her in the first place? Why did he let me sit on the floor beside him in Harrods and laugh as I marched up and down, testing the wheels? I wouldn't have behaved anything like that if I'd known we were buying a case for his girlfriend. And he must have known that. He must have known.

A cold feeling begins to creep over me. This is all wrong.

'All right?' says Luke, turning back to me.

'No,' I hear myself saying. 'No, it's not. You didn't tell me that case was for your girlfriend. You didn't even tell me you had a girlfriend.'