“Computer?” I interject.

“Whatever it is,” she says impatiently. “I told him it would break down and he would lose his job unless he called you.” Her mouth curves into a reminiscent smile. “He moved quite quickly after that. Although, you know, even when he was picking up the card he kept clutching his head and saying to himself, ‘Why am I calling this girl? Why am I doing this?’ So I yelled in his ear, ‘You want to call her! She’s very pretty!’” Sadie tosses her hair back triumphantly. “And so he telephoned you. Aren’t you impressed?”

I gaze back at her, speechless. She’s blackmailed this guy into going on a date with me. She’s messed with his mind. She’s forced him into a romance that he had no intention of pursuing.

She is the only woman I’ve ever known who could make a man call. Ever.

OK, it took supernatural powers, but she did it.

“Great-Aunt Sadie,” I say slowly, “you’re brilliant.”

Sometimes, when I can’t get to sleep, I imagine all the rules I’d invent if I ever got to be in charge of the world. There are quite a few which involve ex-boyfriends, as it happens, and now I’ve got a new one:

Ex-boyfriends shall not be allowed to take another girl back to the special restaurant they used to go to with their previous girlfriend.

I still can’t believe Josh is taking this girl to Bistro Martin. How can he? It’s our place. We had our first date there, for God’s sake. He’s totally betraying all our memories. It’s as if our whole relationship is an Etch A Sketch and he’s deliberately shaking it clean and drawing a new picture, and forgetting all about the old, much better, and more interesting picture which used to be there.

Besides which, we’ve only just broken up. How can he be dating another girl after only six weeks? Doesn’t he know anything? Rushing blindly into a new relationship is never the answer; in fact, it’ll probably make him really unhappy. I could have told him that, if he’d asked me.

It’s twelve-thirty on Saturday and I’ve been sitting here for twenty minutes. I know the restaurant so well, I’ve been able to plan things perfectly. I’m in the corner, tucked out of sight, wearing a baseball cap just to be on the safe side. The restaurant’s one of those bustling brasseries with lots of tables and plants and hooks for coats, so I’m easily able to blend away in the background.

Josh is booked at one of the big wooden tables in the window-I peeked at the reservations list. I have a good view of it from my corner seat, so I’ll be able to study this so-called Marie pretty carefully and watch their body language. Even better, I’ll be able to listen to their conversation, because I’ve bugged the table.

This isn’t a joke-I’ve genuinely bugged it. Three days ago I went online and bought a tiny remote microphone in a pack called My First Spy Kit. When it arrived, I realized it was designed for ten-year-old boys rather than adult ex-girlfriends, as it also came with a plastic Spy’s Log Book and Cool Code Cracker.

But so what? I’ve tested it out and it works! It only has a range of twenty feet, but that’s all I need. As soon as my waiter had taken my drink order, I made a pretext of needing the ladies’ room. Casually, I sauntered past, pretended to drop something, and slapped the tiny sticky pad of the microphone on the underside of the table. The earpiece is hidden under my baseball cap. I just have to switch it on when I’m ready.

And, OK, I know you shouldn’t spy on people. I know I’m doing a morally wrong thing. In fact, I had a big argument with Sadie about it. First she said I shouldn’t come here at all. Then, when it was obvious she was going to lose that one, she said if I was that desperate to know what Josh was going to talk about, I should just sit near the table and eavesdrop. But what’s the difference? If you’re listening in, you’re listening in, whether you’re two feet or ten feet away.

The point is, when it comes to love there’s a different set of morals. All’s fair in love or war. It’s for the greater good. Like those people at Bletchley, cracking German codes. That was an invasion of privacy, too, if you think about it. But they didn’t care, did they?

I have an image of myself, happily married to Josh, sitting around at Sunday lunch and saying to my children, “You know, I very nearly didn’t bug Daddy’s table. And then none of you would be here!”

“I think he’s coming now!” Sadie suddenly says beside me. I finally talked her into being my assistant, although all she’s done so far is wander about the restaurant saying disparaging things about people’s outfits.

I risk a tiny glance toward the door and feel a roller-coaster lurch. Oh God, oh God. Sadie’s right-it’s him. And her. They’re together. Why are they together?

OK, don’t freak out. Don’t imagine them waking up in bed, all sleepy and sex-satisfied. There could be lots of other perfectly reasonable explanations. Maybe they met at the tube or something. I take a deep gulp of wine, then raise my eyes again. I don’t know who to study first, Josh or her.

Her.

She’s blond. Quite skinny, in orange pedal pushers and one of those crisp white sleeveless tops that women wear in ads for low-fat yogurt or toothpaste. The kind of top you can only wear if you’re good at ironing, which just shows how tedious she must be. Her arms are tanned and there are streaks in her hair, as though she’s been on holiday.

As I shift my gaze to Josh, I feel my stomach go all slithery. He’s just… Josh. Same fair floppy hair, same goofy lopsided grin as he greets the maitre-d’, same faded jeans, same canvas sneakers (some cool Japanese label I’ve never quite got the hang of pronouncing), same shirt-

Hang on. I stare at him in disbelieving shock. That’s the shirt I gave him for his birthday.

How can he be doing this? Does he have no heart? He’s wearing my shirt in our place. And he’s smiling at this girl as though no one exists but her. Now he’s taking her arm and making some joke which I can’t hear but makes her throw back her head and laugh with her toothpaste-ad white teeth.

“They look very well suited,” says Sadie brightly in my ear.

“No, they don’t,” I mutter. “Be quiet.”

The maitre-d’ is showing them to the window table. Keeping my head down, I reach into my pocket and switch on the remote control for the microphone.

The sound is faint and buzzy, but I can just about hear his voice.

“… totally wasn’t paying attention. ’Course, it turns out the bloody GPS has sent me to completely the wrong Notre Dame.” He gives her a charming grin and she giggles.

I almost want to leap up from my table, I’m so livid. That’s our anecdote! That happened to us! We ended up at the wrong Notre Dame in Paris and we never saw the real one. Has he forgotten he was with me? Is he just editing me out of his life?

“He looks very happy, don’t you think?” observes Sadie.

“He’s not happy!” I give her a venomous glare. “He’s in total denial.”

They’re ordering a bottle of wine. Great. Now I have to watch them get all merry. I take a few olives and munch disconsolately. Sadie has slid into the seat opposite and is watching me with a trace of pity.

“I warned you, never be a trailer.”

“I’m not being a trailer! I’m… trying to understand him.” I swirl my wine around a few times. “We ended so suddenly. He just cut me off. I wanted to work at our relationship, you know? I wanted to talk things through. Like, was it the commitment thing? Or was there something else? But he wouldn’t. He didn’t give me a chance.”

I glance over at Josh, who is smiling at Marie while the waiter uncorks a bottle. I could be watching our own first date. It was just the same, all smiles and amusing little stories and wine. Where did it go wrong? How did I end up sitting in a corner bugging him?