And the next minute, he’s disappeared into the lift, leaving me alone with my basket and my jumping, unsettling thoughts.

A meeting. What meeting? Why didn’t Mel know about it?

Now I’m envisaging him hurrying into a restaurant where Venetia is waiting, cradling a glass of wine while all the waiters watch admiringly. She gets up, and they kiss, and he says, “Sorry I’m late, my wife turned up—”

No. Stop it. Stop it, Becky.

But I can’t. Thoughts are piling into my head, thicker and faster, like a snowstorm. They’ve been seeing each other every lunch hour. All the Brandon C staff know about it. That’s why Karen and Dawn looked so awkward, that’s why they tried to get rid of me….

The other lift is waiting with its doors open, and on impulse I get in. I reach the ground floor and walk as swiftly as I can manage out of the foyer, ignoring the calls of Karen and Dawn, just in time to see Luke being driven away by his company driver in the Mercedes. Frantically I hail a taxi, step in, and dump the basket on the seat.

“Where to, love?” asks the taxi driver.

I slam the door and lean forward.

“You see that Mercedes up ahead?” I swallow hard. “Follow it.”

I can’t believe I’m actually doing this. I’m tailing Luke through the streets of London. As we drive round Trafalgar Square with the Mercedes in sight, I feel like I’m in some kind of movie. I even find myself glancing through the rear window to check that there are no baddies in pursuit.

“Your boyfriend, is it?” the taxi driver suddenly says in a strong South London accent.

“Husband.”

“Thought as much. Got another woman, ’as ’e?”

I feel a horrible pang in my chest. How did he know? Do I look like the cheated-on partner?

“I’m not sure,” I admit. “Maybe. That’s what I want to find out.”

I sit back and watch a bunch of tourists follow their tour leader across the road. Then it occurs to me that this taxi driver is probably a total expert on people following their partners to prove adultery. He probably drives them all the time! On impulse I lean forward and slide the dividing window across.

“D’you think I should confront him? What do most people do?”

“Depends.” We’ve reached some snarled-up traffic and the taxi driver turns round to face me. He’s got a long face like a sniffer dog, and dark, mournful eyes. “Depends if you want to ’ave an open an’ honest marriage.”

“I do!” I exclaim.

“Fair enough. Risk is that by ’aving it out, you drive ’im into the arms of the other bird.”

“Right,” I say doubtfully. “So…what’s the other option?”

“Turn a blind eye an’ live a sham for the rest of your days.”

Neither option sounds that great.

We’re edging along Oxford Street by now, making slow progress through all the buses and pedestrians. I’m craning my neck, scanning the road ahead, when all of a sudden I glimpse Luke’s Mercedes, turning into a side street.

“There! He went that way!”

“I saw ’im.”

The cabbie deftly changes lanes and a few moments later we’re turning into the same side street. The Mercedes is at the end of the road, turning the corner.

My hands are starting to sweat. It almost felt like a game when I first hailed the cab. But now this is serious. At some point his car is going to stop and he’s going to get out and…then what am I going to do?

We’re winding round the narrow streets of Soho. It’s a bright, sharp autumn day, and a few brave people are sitting out at pavement cafés, cradling cups of coffee. All of a sudden, the taxi driver signals sharply and pulls up behind a van. “They’re stopping.”

I watch, breathless, as the Mercedes comes to a halt on the other side of the road. The driver opens the passenger door and Luke gets out, without even glancing in our direction. He consults a piece of paper, then heads to an unsalubrious-looking brown-painted door. He rings a buzzer and a moment later is admitted.

My gaze travels up to a battered sign hanging from a first-floor window: ROOMS.

Rooms? Luke has taken rooms?

I feel as if something’s clenching me tightly round the chest. Something is going on. Venetia’s up there. She’s waiting for him in a black fur-trimmed negligee.

But why some grotty room in Soho? Why not the Four Seasons, for God’s sake?

Because he’d get spotted. He’s come here because it’s out of the way. It all makes sense….

“Love?” Through a haze I realize the taxi driver is talking to me.