He grinned. ‘You sure are persistent, I’ll give you that. Most of the rest of us gave up asking questions like that long ago.’

‘Why do the Authority care about what happened here? Why do they even need to know any of this stuff?’

‘Maybe they just want to avoid making the same mistakes these people did,’ he said.

And yet, from the way he looked at me, I felt sure he felt the same dissatisfaction.

A day or so later I was back home, the useless data retrieved and our entirely pointless mission accomplished. I had kept waiting throughout for something to go wrong. It didn’t, and I was again reminded just how much of an anomaly my first couple of missions had been, compared to most.

As soon as I got back, I walked into the Hotel du Mauna Loa to get something to eat and found the Godzilla movie had been changed for No Blade of Grass, directed by Cornel Wilde. I watched Nigel Davenport fleeing a motorbike gang across a desolate wasteland as I ate. Winifred and Selwyn were playing Go at a table, and I sipped at a tumbler of grapefruit juice, having lost my taste for alcohol.

Randall Pimms came stomping into the bar just as the film finished. He wore heavy boots, camouflage gear and a fur-trimmed parka, his face streaked with dirt.

‘Jerry!’ Randall cried, clapping me on the shoulder. Winifred flashed him a dirty look from across the room, annoyed to lose her concentration. ‘I swear to God, I’ve been dreaming about beer for the last couple days. Fancy getting me one?’

‘Sure,’ I said, and filled a glass from one of the bottles of home-brew, while Randall hauled himself onto a stool beside my own. I handed the drink to him and watched him swallow most of it down in one go.

‘Where’ve you been?’ I asked, studying the parka. ‘Somewhere cold?’

‘Somewhere hot!’ he exclaimed.

‘Doesn’t that make you a little overdressed?’

He shook his head. ‘Nope. Most of the time we were down in subterranean caverns. Damned cold down there.’

He went on to tell me – and, soon enough, Winifred and Selwyn – about the alternate he had just returned from. Its sun had expanded, starting some time in the Middle Ages in our respective alternates. Much of the surface had been reduced to a lifeless desert beneath the parching heat, but a few tens of millions, despite having to rely on essentially medieval technology, had nonetheless dug deep into the Earth. He described cathedrals and palaces carved into the deep rock over long centuries, and entire cities on a scale to dwarf the Pyramids of Giza, dug deep beneath the earth – much as the Icelanders had done with their Retreat. But then, it seemed, the oceans had themselves turned to desert, and the people had all died, leaving only their cities as monuments to their struggle.