Kerys frowned. ‘That’s interesting. And to him, who is Loki?’

Penny said, ‘The Hatch builders, of course. Whoever gave us the kernels. Whoever’s meddling with our history.’

Ari said, ‘mythic monsters aside, it is Earthshine’s actions that have motivated me to dig deeper into this question of the adjusted histories. Because this was the origin of Earthshine, this extraordinary threat.’ He glanced at Penny. ‘Whether you were prepared to cooperate with my investigations or not.’

Penny smiled, a tired old-lady smile, Mardina thought.

Ari said, ‘What intrigued me particularly about Penny’s own account was not the great leap across realities that she seems to have made aboard the Tatania. It was the smaller, subtler adjustment that she suffered in her own personal history, when a Hatch was first opened on Mercury. An odd case. Nothing but a twist to a personal history.

‘But what is interesting to me was that Penny and her sister managed to find evidence of that limited history change. I mean, other than the memory of Stef Kalinski, who remembered a previous life without a sister. Physical evidence, their mother’s grave marker in Lutetia Parisiorum – or the equivalent city in Penny’s reality – bearing an inscription that mentioned Stef alone, and not the sister. Do you see? A scrap, a trace left behind by an adjustment that was evidently – untidy. Well, with that as a lead, it occurred to me that perhaps, given we have evidence of at least two of these history changes, this world of ours might contain evidence of others. Why not?’

Beth said, ‘And you’ve been looking?’

‘I have. I began a search of archives, of reports from historians and archaeologists. Looking for evidence of structures, documents, even mere inscriptions that might not fit the accepted history. But I soon found I was not working alone.’ And he looked again at Penny.

Penny smiled. ‘Guilty as charged. Now it can be told. I always had an ulterior motive when I set up my Academy of Saint Jonbar. Yes, I taught them mathematics, physics, as per my charter. But I always ran other classes too. History, for example. I claimed that I was using those courses as much to educate myself about your history as the students. But I always tried to make the students think about other possibilities – counterfactuals. Which is an English word that has now been adopted into your language. I see it pop up in scholarly articles.’

‘Yes,’ Kerys said drily. ‘Along with much speculation about the identity of Saint Jonbar.’

‘Who never existed,’ Penny admitted. ‘Not even in my own reality. It’s a term from popular culture, from fiction. A jonbar hinge is a point where history pivots – where the path forks. Well, I always hoped that I would create at least a few bright young scholars who would be predisposed to work in this area. And to look for the kind of evidence Ari describes. We haven’t yet succeeded—’

‘But I have,’ Ari said.

Mardina was no scholar, and usually hated all talk of Before, especially on such a day as this. But she found all this vaguely exciting. ‘It’s like a mystery story.’

Ari smiled at his daughter. ‘It is, isn’t it? And what’s really exciting is that, in time, I found some clues.’

‘Clues?’

‘Not on land, but suitably, for a seafaring nation, under the oceans. Mardina, could you please pass my satchel?’

Penny grumbled, ‘About time you got to the point, druidh.’ She shuffled over to see better.

The satchel contained maps that Ari spread out over the Deputy Prefect’s table. He held his bandage to his mouth, but even so a few spots of bloodied saliva spattered on the parchments.

‘These show coastlines and oceans, as you can see,’ he said, gesturing. ‘It’s well known that the levels of the oceans have risen since, say, the time of Kartimandia. We have historical accounts of inundations and land abandonments, and everybody is familiar with drowned settlements off the modern shores – not least in Pritanike, where vast swathes of land have been lost. But this is true all around the world. In recent centuries the archaeologists have turned their interest to such remains, and have commissioned Navy vessels to support them in their research.

‘Now, in addition to the towns and roads and so forth that we expected to find, given what we read of them in the historical accounts, we have also mapped some much more enigmatic structures, further out from shore. Naturally these are difficult to explore and map—’

‘Spare us your scholarly caution,’ Kerys said. ‘Show us.’

‘The most striking remains are in the Seas of Xin, and in the ocean off our own north-east shore, the Mare Germanicum …’

Mardina and the rest, including Penny who hobbled over with Jiang’s help, crowded around the maps. Mardina saw structures in the offshore oceans, sketched by hand on the printed maps: what looked like tremendous walls, dykes, canals, and what might have been town plans of a particularly stylised kind, concentric circles cut through by radial passages.

Ari let them look. ‘We call this the “Drowned Culture”. It seems to have been a global technology, if not actually a global civilisation – perhaps there were rival empires of a similar level of development, as there are in our world today.’

‘Interesting terminology,’ Penny said. ‘Cultures. Perhaps our own history, then, was the UN-China Culture … The town plans are intriguing, if you study them, as I have. You find the same motif of circles and bars everywhere. Here to the east of the Xin mainland. Here, between Pritanike and Jutland. The “towns”, incidentally, are not systems of roads and walls but mostly extensive systems of drainage ditches and other flood-control measures – just as the Romans have built in Belgica and Germania Inferior, for example. Ways to save the land from the sea, or even to reclaim it once flooded. This seems to have been a civilisation that resisted the sea-level rise, long before that rise even reached the coastlines known to our ancients.’

‘That circle-and-bar motif,’ Penny said. ‘It reminds me of something. Youwei, could you fetch my bag?’

Kerys said, ‘I don’t see why this is so exciting. So here is a culture that evidently vanished, drowned, long before the rise of Brikanti or Rome, the traces lost under the rising sea.’

‘But it’s not as simple as that,’ Ari said, looking pleased with himself. ‘We took a closer look. The Navy teams even sent down divers. They found evidence of war. Bomb craters and burning and the like. These communities seem to have ended in a catastrophic global conflict. For we can date such things, you see, with a little ingenuity, by looking at the thickness of the marine deposits laid down over the ruins in the centuries since—’

‘Yes, yes,’ Kerys said irritably. ‘Just tell us.’

‘The problem is the date, you see. The date of their terrible war. It occurred in the twenty-first century.’

Penny stared. ‘You Brikanti use the Roman calendar.’ She glanced at Beth. ‘That’s the fourteenth century by our timeline.’

Ari pursed his lips. ‘You see the problem? Our own history is robust and complete, a heavily documented and multiply sourced account. This builds on an unbroken tradition of literacy that reaches back three millennia, if not more. There is no mention of walls and cities in the Mare Germanicum a thousand years after Kartimandia and Claudius – certainly no account of a devastating war in the twenty-first century. Xin scholars make similar observations. Here, then, is a set of evidence that does not fit into the history we know. There was another world, dominated by this Drowned Culture, which ended in a terrible war, and somehow our history was – recast—’

‘And not just yours,’ Penny Kalinski said. She was rummaging ineffectually in her bag. ‘Where is that damn slate?’