Back in Kirkwall, we queued for fish and chips, listened to an astronomer in the Peedie Kirk Hall, then repaired to the Reel for local beer, shots of Highland Park, and a clarsach and accordion and an old man's long, strong voice. We fell in with a table of geologists, who talked about stormy weather and the vanished sea of Orkady. That night we slept well in our tent.

In the morning I woke to sunlight stitch-sifted in strings of bright dots, and lay a while before stirring. Yesterday I and Gabrielle had seen a flying object, very much identified, public, known, that matched my long-ago UFO encounter in every respect but size. My hardly original speculation that what Calum and I had seen was some application of advanced secret military technology seemed vindicated. Even the connection with British Avionic Systems, my Man in Black's former employer, was now confirmed. I'd read the excitable tech-press anticipations of this development over the past couple of years, but BAS had kept the thing under wraps until yesterday's test flight. No doubt today's news would be full of it.

I could have looked that up, by rolling over and reaching for my phone. I could have phoned or texted Calum. But I didn't want to. I might get offered a commission to write something about the BAS breakthrough. If I did, I knew I'd pass it up, making some excuse about pressure of other work or lack of expertise (neither of which had ever stopped me writing articles). I even had some expertise, and a continuing low-level interest in UFOs. But the very thought of thinking, writing or talking about the floating silvery globe filled me with dread. As I lay there in Gabrielle's warmth, I tried to understand why.

Gabrielle shifted, stretched, woke. A sleepy smile, a stroking hand.

'Sleep well?'

'Yes,' I said. 'You?'

'Oh yes.'

Somewhere in that brief, phatic exchange, the answer came to me: I wanted to go on sleeping well. I didn't want the dreams to come back.

At Birsay we missed the low tide, and had to be content with a stroll along the shore, where tilted sandstone strata displayed three million years to a single glance, like the riffled pages of an old book. There was a van selling instant coffee, weak and too hot. Then we went to Maes Howe, and in the stone dome followed the guide's words around the walls, peering at inscriptions and Viking graffiti. Stooping in a long tunnel and out into the light, through a stone door whose ton weight had once pivoted to the push of a child's hand.

It was our third September. We were in Orkney for its forty-oddth Science Festival. Out in the Sound the tidal turbines turned. High on the headlands the windmills spun. Lights were on and music was loud. Kirkwall's streets thronged with visitors. Its pubs and halls rang with talk of the New Improvement. Accommodation was nowhere to be had, though we were both on the Festival's programme: Gabrielle taking part in a roundtable on stem cell work, I giving a mid-evening slide-show on a of all things a flying saucers. But we were very minor players: Gabrielle had been chosen as a shining example of what a young researcher could accomplish, and my presence was the almost accidental result of my Sceptics in the Pub evenings at university being remembered by a former fellow student who'd since gone on to great things in the burgeoning sci-com racket. He'd been roped into the festival's organisation, and had a sudden slot to fill due to a bizarre tea-pouring accident that had befallen the scheduled speaker from the Fortean Times.

So we didn't have a room in a hotel or a rented house like the big name speakers did. We had our tent, on a campsite just outside Kirkwall. In that tent, on the night before the fourth day of the festival, I asked Gabrielle to marry me.

She looked at me across the pillow, in the glow of a cold light.

'Yes,' she said, smiling, then raised a finger. 'If ...'

'If what?'

'If I get pregnant.'

I stared at her. 'You want kids?'

'Oh yes,' she said. 'Don't you?'

I thought about it. 'I suppose so.'

'Well then.'

'All right,' I said. 'It's a deal. Is it a deal?'

'Yes,' she said. She grasped my hand, inside the big sleeping bag. 'It used to be called handfasting.'

'Handfasted,' I said, gripping back. 'I like that. So ... when do you want to start?'

'Now is good,' she said.

And it was, but later that night I woke up and found myself stricken with doubt. I was delighted that Gabrielle had agreed to marry me, but to make this conditional on her getting pregnant took some of the shine off it. The proposal seemed instrumental and somehow calculating. I wondered if she knew of the research Nicola had told me about, and was making some canny advance provision. And yet ... and yet ... wasn't she just being honest with me? She wasn't making our relationship conditional on her becoming pregnant, just its legal affirmation. In that light her precondition seemed reasonable enough, even loving a seeking her own advantage to be sure, but suggesting at the same time that what we already had was strong enough not to need formalising.

On the other hand ... and so it went, a long and inconclusive debate in my head, until edges and seams of the tent brightened, and I fell into a sweaty, uneasy, ill-timed sleep. Over breakfast in a cafe in the morning we kept laughing and looking at each other and grinning and reconfirming to each other that it hadn't all been a dream. We walked hand in hand around Kirkwall and I totally surprised Gabrielle by marching into a craft jewellery shop and buying her an engagement ring. As soon as she'd put it on her finger and got her thanks and a big kiss out of the way, she opened out her phone and made a big deal of bookmarking a slew of bridal sites.

'We can save a bit of money on all that,' I said.

'How?'

'Well, you already have the big white dress ...'

'Don't,' she warned, 'even think about saying that again, or it's all off even if it turns out I'm having triplets.'

'Just teasing,' I said.

'I'm not. No way am I going to be anyone's little fairy princess ever again.' She mimed a shudder, then thumbed. 'Hmm, that's more like it ...'

She pointed to an ivory outfit of slinky trousers and a flared peplum jacket.

'Now that,' I said, hardly able to breathe, 'is a look.'

In my memory that September week in Orkney had more days of sunshine and evenings of song and nights of sex than any objective recording could confirm. I remember it as the last of our good times, not because it really was a we had good times after it, and I do remember them. But they're not what you want to hear about now, are they?

18.

I got off the bus just after ten in an April downpour and walked through the long corridor between the front and the back of the hospital that everyone still calls the New Royal. For a few tens of metres from the front entrance there's a display on each side of blown-up, grainy photos and engravings of heroes and heroines of medical history, linked by a once trendy timeline in coded colours. Further on, the corridor widens to a waiting area that's more like a small shopping mall, then narrows again to medical-institutional functionality and opens through glass doors at the far end to the car park at the back.

On the hillside behind the car park, a few hundred metres away by a path across a stream, rises the new BioQuarter. At that time there were six buildings, all newer than the hospital, two of them built in the previous two years. The Stem Cell Centre, where Gabrielle worked and studied, looks like a scale model of that giant glass cube from outer space in which Revelation, as Baxter pointed out to me on his first visit, promises the righteous a happy eternity.

I swiped my card at the barrier in the lobby, nodded to the receptionist, and waited for the lift, gazing idly up at the slowly rotating suspended double-helix stained-glass mobile that filled the atrium at second, third and fourth floor levels. I'd always thought it spectacular but unimaginative. Not that I could think of an alternative, but that wasn't my job. It was the job of some artistic director who hadn't (in my jaded opinion) done it right.

The lift took me to the third floor, where the labs and offices were a the lower two floors housed the building's machinery and stores. I followed the colour-coded carpet to Nicola's place in the open-plan offices of the floor's outer section, which surrounded the glass-walled inner core that contained the labs. (Maintaining this arrangement as anything but a greenhouse accounts, I guess, for a big part of the ground floor's being entirely turned over to machinery, though the air-conditioning's solar power makes it less inefficient than it sounds.) As always on my occasional visits to the centre, I wasn't there to see Gabrielle, although I expected to drop by her desk as usual on my way out. I was there to interview Nicola, this time about new developments in sub-dermal tissue regeneration a funding for a major research project had just been announced. Nicola gave me one of her characteristic sidelights on an otherwise routine story: a nugget about some health bureaucrat who'd had an epiphany on the more radical techniques a hitherto regulated with a heavy hand a after a friend had been badly burned in a car crash.

We talked some more, I took the relevant details and we said goodbye. Then I walked to the area where most of the junior researchers and students, including Gabrielle, worked. Here, desks were more cluttered and personal than in the largely admin area on the other side. Gabrielle wasn't at her desk. Her lab coat was draped on the back of her chair.

'Gone to the Ladies,' said a bearded guy at the adjacent workstation. I nodded and waited. After two minutes I began researching more on the story on my phone a not to my surprise, Baxter's name turned up in connection with it. After ten minutes I started to feel awkward. I wandered off and got another coffee from the machine. By the time I strolled back, Gabrielle was at her desk, hunched over a screen.

'Hi,' I said, laying a hand on her shoulder. She started and turned so violently I almost splashed the coffee. Her cheeks were blotched, the skin around her eyes red amid streaky gaps in her make-up.

'What's wrong?' I asked.

'Nothing,' she said, her voice sullen and lifeless, then added in a firmer, brighter tone, 'Nothing to worry about.' She sniffed hard and smiled. 'Hello. Good to see you.'

I pulled up a wheeled stool, laid down the cup, and sat down.

'What is it?' I said, moving closer and lowering my voice.

Gabrielle glared at me. 'Nothing. Like I said. I was just upset about something. It's nothing to do with you. We can talk about it at home.'

I glanced around. 'Some kind of work trouble?'

'Fuck,' Gabrielle mouthed, in a sort of whispered equivalent of a shout. 'No. Just leave it for now, OK?'

'OK,' I said. I took a sip of coffee. I'd never seen her so distressed. I'd seldom so much as seen her in tears. 'Are you sure?'

'Yes, I'm sure,' she said. Another watery smile. 'We can talk about this at home, all right?'

'Are you sure you don't want to just go home now?' I asked.

'For a fuck's sake,' she said. 'No.'

'All right,' I said, 'but-'

'Just go,' she said.

People were beginning to look. Anyone who didn't know about us a at least half the people there at the time a might have thought I was pestering her. I touched her shoulder a getting another flinch a and left.

We had a rented one-bedroom flat in Leith, overlooking a dusty, noisy, through-route street with a view across the rooftops of matching rundown tenements facing us, of abandoned waterfront debt-boom developments rising like a gap-toothed row of gleaming teeth spotted with the brown of advanced decay, all now being extracted or drilled and filled by racketing looming cranes day and night. Double glazing, venetian blinds, and air-con made that aspect bearable. We'd made the flat our own and comfortable, furnishing it in the then new New Modern style, and decorating it to Gabrielle's taste a to which I happily deferred, recognising it at once as better than mine.

I settled down on a recliner, propped my opened phone on an angled holder, and continued working on Nicola's story and others in my in-progress file. But I couldn't concentrate, despite a welcome lack of interruptions. Every so often I'd stalk to the window, or make another coffee, or flick to the news or get lost in online byways so far removed from my initial query that I couldn't excuse them as research even to myself, or retrace with any conviction how I'd got there at all.

At about 4.30 I saved my inconclusive work for the day and answered some emails. That done, I went through to the kitchen and started preparing dinner. Like most people who'd grown up in the depression, we had still to get over the reflex of regarding meat as a treat. I took some trouble grinding and mixing spices and soaking brown rice for a vegetable curry, knowing that the actual cooking wouldn't take long. By the time Gabrielle arrived at about six the flat was full of the curry's appetising smell and the rice was almost ready.

She shook raindrops off her coat, kicked off her boots, and without saying a word or looking at me padded to the fridge and poured herself a large glass of white wine. I noticed this because she'd been cautious about alcohol in the past few weeks, saying she needed to be fully alert for her work. The timer alarm went off as she raised the glass and gave me a harsh grin. I smiled apologetically and drained the rice, and before I turned back from the sink I realised what had gone wrong that day.

'Oh, Gabrielle,' I said, opening my arms.

'I lost it,' she said, weeping into my chest. 'I lost it.'

Over and over.

I hadn't suspected she was pregnant, and Gabrielle herself hadn't been certain. She had just got round to thinking about buying a pregnancy test kit. Neither of us had any superstitions about foetuses, but we felt the loss of what we hadn't known we had as a small death. We mourned it, then after a time moped intermittently, then recovered, and tried again.

Nothing happened, not even another miscarriage. We each checked ourselves for infertility. The latest over-the-counter kits gave us blue piss: nothing amiss. Neither of us wanted to visit a clinic. We wanted to try everything less invasive first. By the anniversary of our handfasting we were timing our sex lives to a calendar and a clock. At other times we both drank too much. Whisky is a killer. I love it, I still do, but it's easy to love too much. This was another problem we shared, though we didn't think of it that way. We thought of it as a solution, a ready medicine for the small inhibitions that had infiltrated our every move and touch and word.

19.

'You know what our problem is?' said Gabrielle, tipping a splash of water into a fresh-poured Highland Park on the coffee table one of those nights. 'You and me, we're from different species.'

I leaned back into my corner of the vat-grown-leather three-seat sofa a it had been our pride and joy when we'd bought it at Vegan Pelts a and returned her challenging look.

'I know,' I said. 'I've always known. You're a fucking Neanderthal. Look at your dad, it's obvious. Your whole family for that matter.'

I was smiling as I said it, my voice warm to cover the chill I felt inside, the uncanny sense that she had read my mind or independently shared the dark, unavowed suspicion planted in my brain by Calum's thoughtless flight of fancy and Nicola's off-the-record briefing.

Gabrielle shook her head impatiently. 'It's not that, it's serious. Of course it's possible that my family has a tiny fraction more Neanderthal genes than even your average honky. So what? Everyone who's not of the Pure Race has ancestors who fucked Neanderthals, not to mention all the other hominid relatives we've caught hiding in the genome. That's got nothing to do with infertility. Non-Africans have Neanderthal genes because our ancestors could fucking well breed with Neanderthals.'

'That sounds logical,' I said, in my best Spock voice.

'Logical?' She swigged and laughed. 'Yes, this is kind of about logic. It's a pork chop problem.'

I wondered if she'd had a little too much to drink. 'Uh, explain ...'

She leaned forward a bit, an elbow on a knee, glass in the other hand, the bright-eyed didactic Gabrielle I remembered from what now seemed long ago.

'"Pork chop problems",' she said, 'have nothing to do with pork chops. It's sort of a nickname, because Charles Dodgson a Lewis Carroll to you and me a first posed that kind of problem as a string of banal statements about various different guys who eat pork chops, are running out of money, rise early, and so on and so on. The question is about making some statement about one of the guys that follows from the premises. Stating the problem takes less than a page, but Dodgson confessed he couldn't solve it. Turns out you can solve it with some symbolic techniques that Dodgson didn't have available to him, but that's not the point. The point is ...' She paused to sip. 'With me so far?'

'Uh-huh.'

'The point is, Dodgson had put his finger on a very general point, which is that there are all over the place, everywhere, sets of facts we already know or can easily see, but which we can't easily see the implications of. I read this in a book by, uh, William Poundstone, I think. There all kinds of truths that might be interesting, if only we could see them. But we can't, even though all the relevant facts are in plain sight.'

'So,' I said, 'there are all kinds of facts we know or could know, but we can't see what follows from these facts?'

'Got it.'

I frowned. 'Isn't that obvious as soon as it's pointed out?'

'Exactly. It wasn't obvious until Dodgson pointed it out. Or maybe it was Poundstone who clarified what Dodgson had pointed out, which would be kind of another example of what he was saying ... Anyway, what all this has to do with species ...' Her voice trailed off, and she gazed away, as if something interesting were on the blank television screen in the corner.

'Yes?' I prompted.

'Species,' she said. 'And us. And' a her tongue flicked across her lips, and she swallowed hard a 'infertility. Fuck, this is difficult.'

'I know,' I said, laying a hand on her knee. She put her hand across mine, squeezed a little, then shifted her knee and took her hand away.

'Don't make it more difficult,' she said. I felt stung, though I tried not to show it. 'And don't give me that hurt face,' she went on.

'I'm not.'

'You are. Don't tell me I can't see what I see.'

'All right, all right,' I said. I took a small gulp and forced a smile. 'Sorry. You were saying?'

'Yes. What this has to do with species? OK. The human species is breaking up.'

'What?' I closed my eyes tight for a moment, and rubbed my forehead. I didn't want her to know I knew. 'Why do you say that?'

'It's kind of an open secret in genetics,' she said. 'I mean, it's only mentioned in specialist journals and even there it's put ... kind of cagily, right? Because it sort of opens a new can of worms. The human species, right' a she put down her glass to free both hands for gesticulation a 'has become so big, what are we now? Eight billion? Nine? Whatever. And even before then, even back when we were just a billion or so, we were the most numerous species of large mammals on the planet.'