The climate as ever had been the problem. By 2046, six years after the Yellowstone eruption itself and the onset of the volcano winter, things had seemed to be stabilizing, if not actually improving. People did continue to die; Joshua remembered a report that in the end Yellowstone had killed more people from lung diseases caused by the ash than had perished in the immediate aftermath of the eruption itself. But then some climatic tipping point had been reached – some had said it was the collapse of the Gulf Stream, but by then the science data-gathering itself had become too patchy to be sure – and the winter that year had been worse than ever. The rivers froze, the ports iced up, and Midwest farmland submitted to permafrost. When the big hydroelectric plants in Quebec began to fail in the freeze, the American national electricity grid collapsed, and such great cities as Boston and New York had finally to be abandoned.

Across America, people who had clung on to their homes for six years finally gave up and walked or drove out of there, either south across the Datum or stepwise into the Low Earth worlds West or East, where refugee camps had overwhelmed communities that were already struggling to cope. With time new towns had started to emerge, like this one in West 11, towns with a new character, using the scavenged remains of the old and scrambling for new solutions. Timber, plentiful on the Low Earths, was used in fuel-producing gasifiers, like the one on the tractor Joshua could see now – a fuel source that was a lot more accessible, for now, than coal or oil or nuclear. Datum museums had been emptied of nineteenth-century spinning wheels and looms and steam engines, for use as models for new kinds of industry. Electricity was got whatever way you could, such as with alternators and batteries from step-capable vehicles like that golf buggy, fixed to windmills or improvised paddle wheels in rivers. Anything resembling a web was still rare outside the larger, older stepwise cities like Valhalla, but in a town like this there would be walkie-talkies and ham radio set-ups, and maybe somebody would be laying down copper wire for a phone network.

Of course agriculture had been the key, as it had been from the day of the eruption itself – the need to feed all those displaced people. There had been a major international incident when in 2047 the US Navy had raided the Svalbard Global Seed Vault on Spitsbergen, a Norwegian island, for its stock of seeds for heirloom crops – the more primitive, hardier strains needed less cultivation than the varieties that had dominated the vast mechanized fields of the pre-Yellowstone Datum.

But Joshua thought it was working, even if these new patchwork Low Earth towns weren’t quite like any other: neither like their Datum forebears nor even the raw colonial towns of the Long Earth, like Reboot and Hell-Knows-Where. Madison West 11 was always going to be a jumble of old and new. You didn’t drive a car; there were few vehicles on the dirt roads save for farm trucks and ambulances and cop cars and bicycles. You didn’t go online any more, but lined up to deposit your money at bank branches, like the manager was Jimmy Stewart in It’s a Wonderful Life. Yet these quaint 1900-type practices were studded with bits of high tech, such as solar-cell blankets fixed to thatch roofs.

And Datum America itself had not been abandoned altogether, even now. Americans had come to recognize that what they and their ancestors had made of their continent-sized country was a historic monument in itself. So the new worlds had striven to come to the rescue of the old.

Nelson, evidently tiring, had been quiet since they’d sat down here.

Joshua gave him a playful punch on the shoulder. ‘Not far now, old friend.’

Nelson smiled ruefully. ‘I’m glad to have made the trip.’

‘And I’m glad you did too. You always were good company. And you always made me think.’

‘Ouch. Even on your birthday? My deep apologies.’ He glanced sideways at Joshua. ‘Of course, for most of us such occasions mean family and friends. I myself lost contact with my own family in the chaos of the Johannesburg townships, long before Yellowstone. And here you are, Joshua, wandering alone – well, almost alone – on such a significant anniversary.’

Joshua shrugged. ‘I am more domesticated now. Even Sally admits that. But, you know – sometimes I miss the alien. The beagles for instance.’ Dog-like sapients from a very remote Earth. ‘Life gets boring with only humans to talk to.’

‘I thought it was a beagle that chewed off your left hand.’

‘Nobody’s perfect. And he thought he was doing me a favour. As for the rest – well, I do seem to have had trouble building a family.’

‘Perhaps because you did not come from a family yourself,’ Nelson said seriously. ‘Lobsang told me your story, long ago. Your mother, poor Maria Valienté, who gave birth to you alone, and died aged just fifteen. Your father – quite unknown. Of course you were cherished by Agnes and the Sisters at the Home, but that could only be a partial recompense for such a loss, even if you were never really aware of it.’

‘Lobsang did find out something about my mother.’ And had given him one treasured relic, a monkey bracelet, a silly toy belonging to the kid Maria had been when she’d given birth to him … ‘Nothing about my father, though.’

Nelson frowned, looking into the distance. ‘Which is rather unusual, if you think about it.’

‘What do you mean?’

‘I mean that if even Lobsang couldn’t find anything, there must have been deliberate concealment. By somebody, somehow, for some reason.’ He grinned. ‘I’m suddenly intrigued, Joshua. This is the kind of puzzle that has always attracted me. I found Lobsang himself by following a research trail, you know – even though it turned out that he had engineered the whole thing. And since Lobsang has gone, my world has been rather depleted of conspiracy theories.’

Joshua studied him. ‘You’re thinking of researching this, aren’t you?’

Nelson patted his arm, and stiffly got to his feet. ‘Shall we make some more progress? The many candles on that birthday cake won’t blow themselves out.’

‘True enough.’

‘The many, many candles—’

‘I get it, Nelson.’

‘Hmm. But would you like me to follow this up? This business of your father. Think of it as another birthday present. If you would rather I didn’t—’

Joshua forced himself not to hesitate. ‘Do it.’

‘And if I do find something – considering the circumstances of Maria’s brief life, it could be distressing. One never knows, when pulling such a thread, what might unravel.’

‘Well, I’m a grown-up, Nelson.’ But he did remember how much Lobsang’s revelations about his mother had confounded him. ‘Look, I’ll trust your judgement, whatever you find. On my count, one, two—’

They winked stepwise together, with pops of displaced air.

9

EVEN AS THE airship dropped its anchor at the summit of the low hill that dominated the heart of New Springfield, in a stepwise-parallel version of Maine on Earth West 1,217,756, Agnes could see the neighbours coming to call. She felt oddly nervous, as if she had stage fright. This was the moment her new life would begin, she thought, in this late summer of the year 2054 – nine full years after Lobsang’s ‘death’ – in her new home, with these new people.

Ben, three years old, could see the neighbours coming too. If he stood tall and held on to the rail with his chubby hands, he could just about look out of the gondola’s big observation windows without being lifted up, and being an independent little boy that was what he preferred. And as winches whirred, drawing the twain steadily down its anchor cables towards the ground, Ben jumped up and down, excited.

‘Of course they’d come over,’ Sally Linsay said, standing beside Agnes. ‘That’s what folk do. Check out the newcomer. Welcome you, if possible. Make sure you’re no threat, if necessary.’