McGregor pointed. ‘And what the hell did you do to Scotland?’

Ari frowned. ‘We know it as Kaledon. An arena of heroic engineering.’

‘It looks like you demolished mountains,’ McGregor said. ‘Some areas look like they’ve been melted.’

‘Some have been,’ Ari said. ‘A kernel-drive spacecraft, landing or taking off, generates rather a lot of heat.’

‘My God,’ Penny said. ‘They really have brought kernel technology down to the face of the Earth. All that heat energy dumped into the ground, the air. It’s a wonder they haven’t flipped the whole damn planet into some catastrophic greenhouse-warming event, into a Venus.’

‘Maybe,’ Lex said, ‘they were lucky. They got away with it. Just. Perhaps there are other timelines where precisely that happened. Does that make sense, Kalinski? If there are two timelines, why not many?’

‘Or an infinite number.’ She grinned, lopsided. ‘That had occurred to me too. You’re thinking like a scientist, McGregor.’

‘I’ll cut that out immediately.’

Ari followed this exchange closely.

Now the island cluster was passing away to the north-west, and the ship was sailing over the near continent – Gaul to the Romans and the Brikanti, France to the crew of the Tatania. The countryside, where it was spared by the sea-level rise, glowed with urbanisation. But on the track of a broad river Beth made out a neat circular feature, a set of rays spanning out from it, a lunar crater partially overgrown by the green. She pointed. ‘What’s that?’

Ari said, ‘Once a major city of the Roman province. Destroyed in a war some centuries back, by a Xin missile that got through the local defences.’

Penny said, ‘The missile – kernel-tipped? It was, wasn’t it? So it’s true. You people don’t just use kernels as sources of power on Earth. You actually use them in weapons, to fight your Iron Age wars.’

Ari Guthfrithson frowned. ‘Would you have me apologise for my whole history? And is your history so laudable?’

McGregor murmured, ‘We’re missing the point here, Penny. Forget your judgements. We need to learn as much about this world as we can while we’ve got the chance.’

Penny nodded. ‘You’re right, of course, since it looks like we’re going to be stuck here.’ She thought it over. ‘The Ukelwydd is following a high-inclination orbit around the Earth – around Terra. That is, the orbit is tipped up at an angle to the equator—’

‘That is intentional, of course,’ Ari said, ‘so that our track takes us over Pritanike and the landing grounds of Kaledon.’

‘But that means we get to fly over a good span of latitudes. And as the planet turns beneath us, with time we get to look down on a swathe of longitudes too. Give me a few hours with a slate, and I’ll capture what I can. Then with some educated guesswork maybe we can figure out the story of this world …’

CHAPTER 11

Twelve hours later Penny called her companions, with Ari, back to the observation lounge. She’d found a way to project slate images onto a blank wall, and had prepared a digest of her observations of the turning world beneath.

She showed them landscapes of dense urbanisation, the cities glowing nodes in a wider network of roads and urban sprawl. ‘Welcome to Terra,’ she said drily.

‘This is Europa – Europe. Some of the oldest Roman provinces. Give or take the odd invasion from Asia, this whole swathe from the Baltic coast in the north to the Mediterranean in the south has been urbanised continually for more than two thousand years, and the result is what you can see. Many of the denser nodes map on to cities we’re familiar with from our own timeline, which are either successor cities to Roman settlements – like Paris, for instance – or, in places the Romans never reached in our timeline, they follow the geographic logic of their position. Hamburg, Berlin. The nature of the country is different further north, the Danish peninsula, Scandinavia. Just as heavily urbanised, but a different geography.’

‘The heartland of my people,’ Ari said. ‘You may have images of the canal which severs the peninsula from the mainland. A very ancient construction, which was widened extensively when kernels became available.’

Penny goggled. ‘You’re telling me you use kernels to shape landscapes as well? On Earth?’

‘This is Terra, Penny,’ McGregor said evenly. ‘Not Earth. I guess that’s their business.’

Penny showed images now of a desolate coastline, an angry grey sea, ports and industrial cities defiant blights on the grey-brown landscape. ‘This is northern Asia,’ she said. ‘In our reality the Arctic ocean coast of Russia. There never was a Russia here, I don’t believe. But nor is there any sign of a boreal forest at these latitudes. Even the sea looks sterile – nobody fishing out there – and no sign of any Arctic ice, by the way, though we haven’t been able to see all the way to the pole.’

Ari shrugged. ‘It is dead country. It always has been dead. Good only for extraction of minerals, methane for fuel.’

Penny tapped her screen. ‘I’m going to pan south. The extent of the main Roman holdings seems to reach the Urals, roughly. Whereas you have the Xin empire, presumably some descendant of the early Chinese states we know about, extending up from the north of central China through Mongolia and eastern Siberia, all the way to the Bering Strait. In Central Asia, though—’

More craters. A desolate, lifeless landscape.

This made Beth gasp. ‘What happened here?’

Ari sighed. ‘The steppe was historically always a problem. A source of ferocious nomadic herdsmen and warriors, who, whenever the weather took a turn for the worst, would come bursting out of their heartland to ravage the urban communities to west and east. Finally Xin and Rome agreed to administer those worthless plains as a kind of joint protectorate. It is an arrangement that worked quite well, for centuries. Mostly.’

McGregor’s grin was cold. ‘Mostly?’

‘Wherever two great empires clash directly there will be war. And when weapons such as the kernels are available – well. You can see the result.’

Penny said, ‘Here’s the Xin homeland. Again there seems to be a historical continuity with the cities and nations we know about from the early first millennium …’

Some of the images had been taken at night. Half a continent glowed, a network of light embedded with jewel-like cities – and yet here and there Beth could see the distinctive circular holes of darkness that must be relics of kernel strikes.

Ari was watching Beth, as much as he was following the images. ‘Your reaction is different from the others. You seem – dismayed.’

‘That’s one word for it. I grew up on an empty world.’

‘Ah. Whereas all this, in comparison, billions of us crammed into vast developments—’

‘How do you breathe? How do you find dignity?’

‘You mean, how will you live here.’ He smiled. ‘Beth Eden Jones, you, of all the crew of the Tatania, are by far the most intriguing to me. The most complicated. If fortune allows it, I hope to be able to help you find a place in this, the third world you have had to learn to call home …’

Penny said now, ‘As Ari has told us, the rest of the world is a kind of playpen for the three superpowers of Eurasia. Here’s Australia.’

Beth saw arid crimson plains like a vision of Mars, pocked with the circular scars of explosions, the rectangular wounds of tremendous mines.

‘Mined by the Xin,’ Ari said.

‘My mother was from Australia,’ Beth said. ‘I visited once. What happened to the native people here?’

Ari looked at her curiously. ‘What native people?’

‘Africa,’ Penny announced, pulling up image after image. ‘To the south, extensive mining and farming by the Xin, it seems. To the north, the Sahara – but look at it …’

The desert was covered by a grid of huge rectilinear canals.