‘Now Bozeman, Idaho, is at one with Pompeii. It will take years for the ash fall even to cool, let alone for the land to be reclaimed by humans.’

‘Yet something’s growing down there,’ Joshua said. Peering down, he pointed out scraps of green.

Lobsang was silent a moment; Joshua imagined his artificial senses trained on the ground below. ‘Yes. Lichen. Moss. Even lodgepole pines. Just saplings, but still – the resilience of life.’

The twain turned its nose and headed south, towards the caldera itself.

‘So, Lobsang. Yesterday you told me you were disturbed by a plague of common sense breaking out across the planet? It would be a first, I grant you.’

‘I can give you examples . . .’

The screens in the deck flashed up with brief video snips of tales from across the US during the days and years of the Yellowstone disaster:

One little kid in a first-school classroom in Colorado, his teachers having succumbed to an ash infall, quietly organizing his hysterical classmates and walking them out of the building in a line, heads wrapped in wet towels, hands on the shoulders of the person in front.

A young teenager stuck with her grandparents in a care home in Idaho, full of old folks who couldn’t or wouldn’t step, calmly working out rotas of food sharing and mutual care.

A well-off family in Montana, the mother refusing to leave their home with her surviving children because of one little girl lost, and obviously killed, in the wreckage of an ash-crushed conservatory – her husband going crazy with fear and refusing to stay to dig out the wreck – and an au pair, a girl no more than seventeen years old, organizing the family to dig out the lost one and carry out the body, as that was the only way to persuade the mother to move and save the rest.

Joshua remembered stories he’d heard himself, one from Bozeman in fact, an account of a ‘sensible young lady’ who had come around with dazzlingly smart advice on how to survive the eruption.

‘These anecdotes all involve very young people,’ he observed. ‘If not children.’

‘Indeed. And you’ll note that their exploits are not characterized by heroism, or great feats of endurance, or whatever. Instead they are calm, and full of wise leadership – certainly wise for their age. Good judgement, whose value is evident enough even for the adults around them. And a certain cold rationality. They are able to set aside the kind of illusion that comforts but baffles the regular human mind. Consider the woman in Montana with the dead child. She couldn’t accept the death. The au pair not only accepted it; she accepted she wasn’t going to be able to persuade the mother otherwise, and came up with a strategy to save the family taking that bit of psychology into account.’

‘Hmm.’ Joshua studied the ambulant’s inexpressive face. ‘What are you suggesting, Lobsang? You’ve talked about this before. Are we seeing the emergence of some kind of smarter breed? True Homo sapiens, you’ve always called them – as opposed to regular mankind, a bunch of apes who call ourselves wise . . .’

‘Well, it looks that way. If you are prepared to build a mountain of hypothesis on a raft of a few observations.’

But Lobsang, Joshua suspected, would have more behind his argument than a few scattered fragments of evidence like this. ‘So how is this happening? And why now?’

‘I suspect those two questions may be linked. There may be some – incubator, somewhere out in the Long Earth. Only now, you see, with the advent of widespread stepping, have the products of such an incubator been able to reach the Datum. And perhaps we are seeing the emergence of this new quality under stress. Some gene complex suddenly expressing itself, under the pressure caused by the huge dislocation after Yellowstone. That would explain why we see this now, you see. And then there’s you, Joshua.’

‘Me?’

‘Your headaches. This odd psi sense you seem to have for the presence of an unusual kind of mind – and a powerful one. If I screwed a lightbulb in your ear I suspect it would start flashing a red alert.’

‘Nice image. Something new in the world, or the worlds, then. And something I’m sensitive to, like I was sensitive to First Person Singular.’

‘Not only that, there may be a nascent organization behind it all.’

‘An organization? Doing what?’

‘My colleague Nelson Azikiwe has an account of an English child – his family are refugees in Italy now – another disturbingly bright child, but this one terrorized by fearful locals. There had even been mutterings of witchcraft. His parents, it seems, were approached by another, a teenager. They were offered a scholarship at some kind of residential college, such was the teenager’s story, aimed at exceptionally bright children. The parents’ account was vague, but they were struck by the eerie calmness of the youngster, the effortless way he seemed to dispose of their objections to his plan.’

‘Did they let their son go?’

‘With some teenager? Of course not. Although, Nelson says, he almost convinced them. Nelson predicts the next approach will be through a front, a more reassuringly elderly adult . . .’

‘If this is all so, what do you want to do about it, Lobsang?’

‘If this nebulous entity exists, if some new kind of human being is emerging in our world, I want to meet it. Talk to it. I see myself as something of a guardian of mankind, Joshua. This new entity may be reaching the end of its own long childhood. As it rises up to adulthood, I want to make sure it means us no harm.’

‘And that, I imagine, is where you want my help. Finding these new people.’

‘You and a number of others. Ah . . . It is time.’

‘For what?’

All the display screens cleared down. ‘Look out of the windows.’

For some time the ground had been steadily rising, but it was a fractured ground, ash-blanketed, strewn with immense rocks. It was as if, Joshua thought, they were following debris rays towards a great lunar crater.

Quite abruptly the ground fell away, as if they had sailed over a cliff. Joshua looked down to see a landscape like some gloomy artist’s palette: swirls of reddish rock, lava pools that bubbled languidly, sulphur-yellow scum beneath wraiths of steam. His view was obscured by heat shimmer, and he heard switches being thrown in the gondola’s air conditioning unit, as suddenly, after hours of fighting off arctic chill, now it strove to exclude the sudden warmth.

And when he looked ahead, beyond the curdled plain below, he saw a kind of cliff face, very far off, blued by the mist of distance, shimmering in heat haze.

Lobsang said, ‘This is the caldera, Joshua. The crater. So big you can’t really see that it’s circular from here. The ground, below, is half a mile down – we’re above the collapsed magma chamber. And the caldera’s far wall is over forty miles away. We were unlucky actually.’

‘Unlucky?’

‘The supervolcano erupts every half million years or so. Some eruptions are worse than others – in some, more magma is released, more damage is done. This was the worst for two million years. The geologists were able to tell us that much, even though they didn’t see it coming. And the result lies around you.’

Joshua had no words.

‘Impressive, isn’t it? Even to God, it must be quite a sight. Even to me . . .’ His voice wavered oddly.

Joshua felt a flicker of concern. ‘Lobsang? Are you all right?’

Lobsang didn’t answer. But he said, more uncertainly, ‘I don’t ask this of you lightly, Joshua. To travel again, I mean. I have become more aware of the risks I ask you to take when stepping into the Long Earth. Any of us.’

‘What do you mean?’

‘Have you considered what would happen were you to die out there? I’m referring to the fate of your immortal soul. Can a discarnate soul cross stepwise between the worlds? If you were alone – in a world in which there were no other humans to host your spirit – you might not be able to reincarnate as a human at all.’