After a short drive, we get out on a street corner in Vauxhall. Vauxhall? This is all very unlikely.

‘What?’ I begin, looking around. ‘Where are we—’

‘Ssh.’ Dan cuts me off. ‘This way.’

He leads me briskly through an unfamiliar garden square, just as though he’s been here a million times. He ushers me past the church in the corner. We walk through the little graveyard and approach an old wooden gate, set in a brick wall, with a keypad next to it.

‘OK,’ says Dan to himself as we come to a halt. ‘The only question is, have they changed the code?’

I’m too bemused to answer. Where the hell are we?

Dan punches in a code, and I hear an unlocking sound from the gate. Then he slowly pushes it open. And I don’t believe it: it’s a garden. A totally deserted little garden. I stare ahead, open-mouthed, and Dan surveys me with a twinkle of satisfaction.

‘Surprise,’ he says.

I follow him in, looking around in wonderment. What is this place? There are raised beds. Trellises. Pleached apple trees. Roses. It’s a little haven in the heart of London. And in the centre of it all is an arrangement of five abstract modern sculptures – all twisting, sinuous, hardwood curves.

It’s towards these that Dan is leading me, authoritatively, as though he owns the place. Without speaking, he pushes me up against a sculpture and starts to kiss me with determination, peeling off my coat, cupping my naked breasts, not saying a word. The smooth sweep of the sculpture melds to me perfectly. The air is fresh against my skin. I can smell roses in the air; hear the laughter of passers-by on the other side of the wall. They’ve got no idea what we’re up to. This is surreal.

I want to ask, ‘Where are we?’ and ‘How did you know about this place?’ and ‘Why haven’t we been here before?’ but already Dan is pulling me on to another of the sculptures. He fits my limbs expertly to its curves as though it’s custom-made. For thirty seconds he just stares at me, splayed on the wood, like his own private boudoir shot. A million miles from white suspenders and Prosecco.

Then he’s stripping off his own clothes, no pausing, no hesitating, no wondering, his face urgent. Businesslike. Serious. Was this sculpture designed for sex? I can’t help wondering. And how does Dan know about it? And what – why …?

Moments later, I inhale in shock as Dan bodily lifts me on to a third, even more strangely curved sculpture. With firm hands, still not speaking, he manoeuvres me into the weirdest ever … Wait, what does he want me to do? I’m getting head rush. My limbs are twitching in this unfamiliar position. I’ve never known … How did he even think of … If the boudoir shots were ‘soft’, this is full-on, 18-rated …

I had no idea Dan even …

Oh God. My thoughts putter out. I can hear my breath coming in short gasps. I’m clutching hard at the wood. I’m going to explode. This isn’t ‘surprise’. This is ‘seismic’.

I don’t think I’ve ever felt so sated in my life. I’m almost shaky. What was that?

When we’re finally, finally done, we nestle in the curve of one of the sculptures (they are so designed for sex) and stare up into the sky. There aren’t any stars to speak of – too cloudy – but there’s the floral, earthy scent of the garden and the trickle of a water feature that I didn’t notice before.

‘Wow,’ I say at last. ‘Best surprise ever. You win.’

‘Well, if you will dress up like a hooker.’ I can sense Dan grinning into the darkness.

‘So, what is this place?’ I gesture around with a bare arm. ‘How did you know about it?’

‘I just knew about it. It’s great, isn’t it?’

I nod, feeling my heart rate subside. ‘Amazing.’ I’m still suffused with a rosy glow, with endorphins coursing round my body. (Do I mean pheromones? Sexy loving hormones, anyway.) In fact, I feel pretty euphoric. Finally it’s all worked out! Project Surprise Me has led to this astounding, sublime and transcendental evening which we’ll remember forever. I feel so connected to Dan right now. When’s the last time we lay naked in the fresh night air? We should do this more. All the time.

How did he know about this place, anyway? I think idly. He didn’t really answer the question.

I nudge Dan. ‘How exactly did you know about it?’

‘Oh,’ says Dan, yawning. ‘Well, in actual fact, I helped to create it.’

‘You what?’ I raise myself on an elbow to stare at him.

‘During university, the summer after my first year. I volunteered for a while.’ He shrugs. ‘It’s a community garden. They let groups in to study horticulture, herbology, that kind of thing.’

‘But … how come? Why a garden?’

‘Well,’ Dan says, as though it’s obvious, ‘you know I’m into gardening.’

I know what?

‘No I don’t.’ I peer at him in astonishment. ‘What do you mean, “I’m into gardening”? You’ve never been into gardening. You never garden at home.’

‘That’s true.’ Dan makes a regretful face. ‘Too busy with work, I suppose. And the twins. And now our garden’s basically a playground, what with the Wendy houses.’

‘Right.’ I pull my coat around my shoulders, digesting this. ‘My husband, the gardener. I never knew.’

‘It’s not a big thing.’ Dan shrugs. ‘Maybe I’ll take it up again when I retire.’

‘But wait.’ A fresh thought strikes me. ‘How did you know these sculptures were so … fit for purpose?’

‘I didn’t,’ says Dan. ‘But I always looked at them and wondered.’ He twinkles at me wickedly. ‘I wondered a lot.’

‘Ha.’ I smile back, running an affectionate hand over his shoulder. ‘I wish I’d been your girlfriend back then. But that year …’ I wrinkle my brow, trying to remember. ‘Yes. I was attached.’

‘Well, so was I,’ says Dan. ‘And I don’t wish we’d known each other back then. I think we found each other at exactly the right time.’ He kisses me tenderly and I smile absently back. But my brain is snagging on something. He was attached?

‘Who were you attached to?’ I ask, puzzled. My mind is already running through the roster of Dan’s previous girlfriends. (I’ve quizzed him quite extensively on this subject.) ‘Charlotte? Amanda?’

Surely neither of those works, timing-wise?

‘Actually, no.’ He stretches, with another huge yawn, then pulls me closer. ‘Does it matter who it was?’

My mind tussles with two answers. The not-ruining-the-moment answer: no. And the I-have-to-know-this answer: yes.

‘It doesn’t matter,’ I say at last in a light, breezy tone. ‘I’m not saying it matters. I’m just wondering. Who it was.’

‘Mary.’

He smiles at me and kisses my forehead, but I don’t react. All my internal radar has sprung into action. Mary? Mary?

‘Mary?’ I try a little laugh. ‘I don’t remember you mentioning a Mary, ever.’

‘I’m sure I told you about her,’ he says easily.

‘No you didn’t.’

‘I’m sure I did.’

‘You didn’t.’ There’s a hint of steel in my voice. I have all Dan’s former girlfriends logged in my brain, in the same way that FBI agents have America’s Most Wanted. There is not and has never been a Mary. Until now.

‘Well, maybe I forgot about her,’ says Dan. ‘To be honest, I’d forgotten about this place. I’d forgotten about that whole part of my life. It was only when you said, “something adventurous” …’ He leans over me again, his eyes mischievous. ‘It woke something up in me.’

‘Clearly!’ I say, matching his tone, deciding to leave the issue of Mary. ‘Come on then, give me a tour.’

As Dan leads me around the paths, gesturing at plants, I’m slightly gobsmacked at his knowledge. I thought I knew Dan inside out. And yet here’s this rich seam of passion which he’s never shared with me.

I mean, it’s great, because we could definitely do more with our own garden. We can turn it into a family hobby. He can teach the girls to weed … hoe … And presents! Yes! I have to resist a sudden urge to fist-pump. All his presents are solved for the next twenty years! I can buy him gardening tools and plants and all those witty items saying ‘Head Gardener’.

But I must bone up on gardening myself. As we progress, I’m realizing quite how inexpert I am. I keep thinking he’s talking about a shrub when he’s referring to a climber, or vice versa. (The Latin names really don’t help.)

‘Amazing tree,’ I say as we reach the far corner. (I can get ‘tree’ right.)

‘That was Mary’s idea.’ Dan’s eyes soften. ‘She had a thing about hawthorn trees.’

‘Right,’ I say, forcing a polite smile. This is the third time he’s mentioned Mary. ‘Gorgeous. And that arbour is lovely! I didn’t even notice it at first, tucked away there.’

‘Mary and I put that up,’ says Dan reminiscently, patting the wooden structure. ‘We used reclaimed wood. It took us a whole weekend.’

‘Well done, Mary!’ I say sarcastically, before I can stop myself, and Dan turns his head in surprise. ‘I mean … amazing!’

I link my arm in Dan’s and smile up at him, to cover the fact that all these little mentions of Mary are feeling like pinpricks of irritation. For a woman I’d never even heard about three minutes ago, she seems to be remarkably present in our conversation.

‘So, was it serious, you and Mary?’ I can’t help asking.

Dan nods. ‘It was, for a bit. But she was studying at Manchester, which is why we broke up eventually, I guess.’ He shrugs. ‘Long way from Exeter.’

They didn’t break up because they had a row or slept with other people, I register silently. It was logistics.

‘We had all kinds of dreams,’ Dan continues. ‘We were going to set up a smallholding together. Organic veg, that kind of thing. Change the world. Like I say, it was a different me.’ Dan looks around the garden and shakes his head with a wry smile. ‘Coming in here is strange. It’s taken me back to the person I was then.’