‘Both cacti and trees photosynthesize busily – that is, they use the energy of sunlight to grow. And the photosynthesis, by the way, is a form known from Earth; as seems obvious, life on this Mars has been seeded from Earth.’

Sally frowned. ‘I don’t understand. This is the Gap. There is no Earth here.’

‘Ah, but there are Earths close by . . .’

When it was young, he said, Mars – every version of Mars – was most likely warm and wet, with a thick blanket of air, and deep oceans. It had been like Earth in many ways – indeed, more generous in those days, and the biologists believed that even complex life, plants, something like animals, might well have got kick-started here on this generous young world within the first billion years or so. It had taken billions more years on Earth.

But Mars was smaller than the Earth and further from the sun, and those facts doomed it. As the geology seized up and the volcanoes died back, and the sunlight got to work breaking up the upper atmosphere, Mars lost a lot of its air. Its water froze out at the poles, or receded to buried permafrost or deep underground aquifers.

‘That is how it was on the Mars of Datum Earth, and on most other versions of the planet. But here, you see, this Mars has evidently had a regular injection of living things from the neighbouring stepwise Earths.

‘Think about it. In our home reality, it was believed that life could be transferred between Earth and Mars, or vice versa, by the great splashes of meteorite impacts. This was called panspermia: the natural propagation of life from one world to the next. But in the Gap, well, there’s no originating Earth, but for the last few million years at least there have been stepping sapients. And every time a hapless humanoid falls from a stepwise Earth into the Gap, it may be destroyed by the vacuum, but some of the freight of microorganisms it carries will survive, delivered into space with so much less effort than a lethal rock splash. And some of those microbial travellers will survive to seed Mars – not just once, but again and again.’

‘I see. I think. Ticks from unlucky trolls, colonizing Mars!’

‘More likely stomach bacteria, but yes. If life gets the chance it will proliferate where the water is, in the surface ice, the permafrost, the aquifers. In time great feedback loops would be established – just as on Earth, in fact – living things mediating cycles of mass and energy, and in particular water. This Mars has very similar, if not identical, geology and physics to the Mars of the Datum. It is life that has made it as clement as it is, by mobilizing the water and other volatiles. Earth life helped restore the climate – and made it possible for Mars life, the older natives, to flourish. But all this is unusual, you see. Only happened because of the Gap. In the language of the Long Earth, this Mars is a Joker, an exception among Marses.’

‘But wonderful nonetheless,’ Sally said.

‘Oh, yes. But not our discovery, unfortunately. The Chinese discovered a second Gap in the East, five years ago, and observed the same kind of life-spreading mechanism in that solar system. The Chinese! Typical. But even without panspermia, on all the Marses, we think, traces of that original native suite of complex life might survive, as spores, seeds, cysts . . . Who knows? Waiting to be woken up, like Sleeping Beauty, with a kiss of warmth and water.’

‘Is that possible?’

He winked. ‘Ask your father about life on Mars.’

As the Martian night closed in, the crew of Marsograd, with Sally, withdrew to the galley, the cosiest location. Here they ate another meal, the centrepiece of which was thick steaks of prized alpaca meat, with boiled greenhouse-rhubarb for a sweet, and they drank more coffee, and more vodka, most of which Sally resisted.

Sally felt curiously drawn to these three odd fellows in their shabby hovels. They seemed to have a clear sense of mission. Maybe it was just that she had become so disillusioned with mankind, from the examples she encountered too often. The Long Earth was, in a way, too easy a place to get to; it was only after some bunch of idiots had already built their spanking new town slap in the middle of the flood plain of a stepwise Mississippi, and the waters had started to rise, or whatever, that they generally came to Sally’s attention. Whereas these Russians had come to a place that was supremely hard to survive in, even to get to, and were now showing supreme intelligence, in their slob-like way, in learning about their environment and how to live in it.

But their tragedy was of course that the country that had given them this mission had all but collapsed.

Alexei Krilov’s main beef about that seemed to be that the academies to which he would have reported his science results were moribund, if not defunct. ‘Nobody to read my papers. No universities to give me tenured posts and science prizes. Poor Alexei.’

Viktor, already drunk, snorted dismissal. ‘Academies? On Datum, whole of Russia abandoned now. Gone. Moscow under ice. Polar bears in Red Square. And parties of Chinese working their way in from Vladivostok.’

Sergei had spoken little. ‘Chinese bastards,’ he growled now.

‘Ha! We are last Russian citizens, like cosmonaut in Mir station when Union collapsed, last Soviet citizen.’

‘It’s not as bad as that,’ Sally said. ‘Sure, Datum Russia is pretty much uninhabitable now. But most of the population escaped to the Low Earth footprints. The Long Russia survives.’

Viktor grunted. ‘Sure. Where struggle to build country begins all over again. Just like after Mongols smashed Kiev. And Napoleon smashed Moscow. And Hitler smashed Stalingrad.’ He wagged his half-empty glass at Sally. ‘We Russians have saying: “First five hundred years are worst.” Cheers.’ He drained his glass, refilled it from the flask.

‘Chinese bastards!’ Sergei shouted now.

Viktor patted Sergei’s arm. ‘There, there, big fellow. Pah! Let Chinese have frozen ruins of Datum. To us, Long Earth, Long Mars – and the stars!’

They drank a toast to that. Then to the Nobel Prize that Alexei was never going to win. Then to the soul of the alpaca whose life had been sacrificed to provide the steaks they had enjoyed.

And then they tried to teach Sally the words of the Russian national anthem, in English and Russian. She crept out to go to bed at the point they’d got on to the third verse: ‘Our strength is derived through our loyalty to the Fatherland. Thus it was, thus it is and thus it always will be! . . .’

18

IT WAS A YEAR after that first meeting in Happy Landings that Joshua next came across Paul Spencer Wagoner – this time, in Madison West 5.

‘Hello, Mr Valienté!’

Joshua was standing with Sister Georgina, in the small graveyard outside the Home that his old friend had run at that point. After the Madison bombing the Home had been painstakingly reestablished here in West 5, and the new graveyard held just two stones. The most recent was for Sister Serendipity, a lover of cooking whose enthusiasms had always lit up Joshua’s young life – and who, according to Home legend, had been on the run from the FBI. It had been Serendipity’s funeral that had brought him here, in fact.

And now Paul’s bright voice, older but unmistakable, called to him from across the street.

With Sister Georgina, Joshua crossed the road. It took a while; Georgina was another veteran of Joshua’s childhood days, and was almost as old as Serendipity had been.

Paul Spencer Wagoner, now six years old, was standing there with his father. They both looked uncomfortable, Joshua thought, in new-looking Datum-manufacture clothes. But Paul had a black eye and a swollen cheek, and his dark hair looked odd to Joshua, as if roughly cut. Joshua’s own little boy, Daniel Rodney, was just a couple of months old, and the Sisters had been cooing over the images Joshua had brought home for them. And there was enough of a father’s soul in Joshua now to make him wince at the trouble Paul, still a very young boy, was evidently having.