There ended my pathetic words of caution – I was powerless to her by then, if that’s not already self-evident. It was the weirdest feeling, a stomach-dropping arousal, the city diminished and out of reach, until the towers and the Dome and the docks, the airport runway and the ribbon of river all lost their meaning entirely and I closed my eyes and succumbed.

Then, a sudden, aching removal, Melia’s voice in interruption: ‘Don’t freak, but I think we’ve stopped.’

She struggled up to sit next to me and brushed the dust from her knees. I zipped myself up. The gondola was still. In the next car along, a man stood and looked back at us. I had no idea if he’d been able to see what we were doing. None of us made any sign.

‘I’m sure it’s okay,’ Melia said. Her arms encircled me. ‘Is it because of us?’ she whispered, as if there were microphones in the car.

‘I don’t know.’ Oh, the solipsism of us, as if a couple enjoying each other could cause an entire transport link to grind to a halt. It took a moment to realize I was holding my breath, as if to hold the silence, hold us safe. I thought, If the winds were stronger, would we sway and creak? What would it feel like to know you were about to plunge three hundred feet to the river? Would the doors spring open on impact or would we be sealed, figures in a snow globe?

‘We’re moving again,’ Melia breathed.

And we sat side by side, backs straight, fingers entwined, for the rest of the ride, neither speaking; it seemed to me our breathing was synchronized. When we disembarked, I avoided the eyes of staff, but Melia thanked them, gleefully innocent. ‘See? No arrest. No one’s interested in us, Jamie.’ She led me back through the station and out onto the concourse. ‘The point is, did you feel claustrophobic?’

‘Not claustrophobia, exactly, no. It was more a fear of falling.’ I steered her into the shadows. ‘How about you?’

‘The same. Like it was going to come loose and we’d just drop like a stone. I’m calling that progress: we replaced our phobias with a new one!’ She punched the air, her exhilaration contagious. ‘I feel something else new,’ she whispered, and her face was close to mine, her eyes wide and confessional. ‘I won’t say it, though. It’s too soon. Too crazy.’

‘Say what?’

‘You know.’ Kissing my cheek, exactly as if we were friends saying goodbye after a chance meeting, she turned and walked away from me, past the ticket office, in the direction of the Tube.

I remained where I was. What was going on here? Living a lie was one thing, forging a secret subplot, but this was becoming the main plot, the truth. For the first time, we’d taken our affair outside. Our aborted sex act might have been high above the city but it was still public transport, with cameras, possibly even with another passenger watching. It had been an appalling risk, an act of lunacy, unless . . .

Unless we were edging now towards wanting to be caught. Wanting to be asked to choose.

And, if we were, would we make the same choice?

I walked the short distance to the ferry pier in a fugue, glad that there was no one on the boat to St Mary’s for me to have to talk to, to ask me what I was doing getting on here, or even just if I’d had a good day because theirs had been terrible. I could taste the gin in the warm cabin air, hear the chimes of bottles as the assistant restocked the fridge with beers.

As we docked at St Mary’s, I looked back to the peninsula and Canary Wharf beyond, the towers silhouetted against the late dusk sky; in the foreground, the red-eyed sentinels of the Thames Barrier. I realized I felt as happy as I’d ever felt. I felt elated.

Then, moments later, I got a shock. Not far from the pier, a few steps down Artillery Passage past Mariners, I saw Kit. He was with a tall, bony guy in jeans and trainers, a pair of oversized headphones around his long neck like a scarf. I assumed he was a mate, though by the time I’d reached Prospect Square, I’d convinced myself he was Kit’s dealer.

Head down, I hurried past before he could see me, before he could summon me close enough to smell his wife’s saliva dry on my skin.

*

The next morning, Kit arrived on the boat eating a doughnut oozing peanut butter and jam, scoffing it in that way people did when their body has been starved of nutrients the night before.

‘I thought I saw you outside Mariners last night,’ I said. ‘About ten o’clock?’

As I kicked myself – what if we’d in fact been on the same boat and he’d half-noticed me get on at the peninsula and only now had his memory jogged? – he merely shrugged.

‘You were with some guy,’ I added.

‘Give me a break, Jay, it’s not like we’re exclusive.’ This he said in a theatrically camp tone, his breath smelling of peanut butter. His eyes were rimmed red, pink lines patterned the white.

‘I just thought he looked a bit dodgy, that’s all.’

‘Maybe dodgy by your standards.’ But he didn’t say who the guy was and, next thing, Steve had boarded and was drawing our attention to a black figure crawling like a monster insect on the slanted roof of one of the waterside towers.

‘Suicide?’ Kit said, without concern.

Steve chuckled at his heartlessness. ‘No, you Good Samaritan, you. He’s a cleaner.’

‘Or a technician of some sort,’ I said, ‘fixing something on the exterior.’

‘How the hell is he attached?’ asked Kit.

‘Ropes,’ Steve said. ‘I read about it the other day. They work on skyscrapers and bridges, crazy places. I bet they get danger money.’

‘I bet they don’t,’ Kit said glumly. ‘I bet they get paid a fucking pittance.’

‘Don’t get him started on money,’ I told Steve.

‘Don’t get him started on being a twat,’ Kit said, his expression clouding.

Admittedly, I’d been a little thoughtless, but I didn’t think I deserved that. What was his problem? When Gretchen arrived, he moved away from us, throwing me an unfriendly look.

‘What’s eating Gilbert Grape?’ I said to the others. ‘Hangover?’

‘It must be because he didn’t get that promotion,’ Gretchen said.

‘What promotion?’

‘Oh, Jamie, he told us all about it yesterday.’ ‘I got a different boat home,’ I reminded her.

‘I’ll see if he wants to come out for a smoke,’ Steve said and Gretchen said she’d come too.

‘Make sure you stand one on either side, you don’t want him jumping in,’ I joked, but neither of them cracked a smile. I sighed. I knew Kit better than they did and even though he’d made that reference just now to suicide, he would never attempt it himself, especially not over some work setback. Some other commuter might, though. Any one of them could board alone one night after a work disaster, wait for the boat to reach a stretch of particularly evil-looking currents, then stroll out onto the deck and find a spot to do it. Just drop overboard without a word, never to be heard of again.

But, no, the crew kept count. I’d been aware of them using those handheld clicker devices every time I crossed the gangway: it was maritime law probably. If the numbers didn’t tally, they’d know soon enough.