This is what I had learned from Ernest Schultner during my most recent mission briefing, when he sketched out the broad details by which this particular alternate had met its end.

Some years before, a brown dwarf star had entered this world’s solar system. Over a period of several years, that ball of cold inert gas, not much smaller than Neptune, had crossed the ecliptic plane at a steep angle before becoming caught in the sun’s gravity well. It had looped around the sun once and was then thrown back towards the outer reaches of the solar system.

On its way back out, this dwarf star – named Shiva by the astronomers tracking its progress – had passed close enough to Earth to yank it out of its normal orbit and send it slowly spiralling outwards, into a new orbit that lay much, much farther from the sun. They’d known almost from the moment Shiva showed up in their lenses just what was coming to them. And once it became public knowledge, anyone with a rudimentary grasp of orbital mechanics was able to come to the same conclusion: their world was coming to a terrible end.

When it finally happened, being literally dragged out of its regular orbit triggered unprecedented earthquakes right across the globe. Schultner had shown me recovered footage of vast tsunamis sweeping across continents, of terrible storms ravaging cities all over the planet. The few who lived through it got to enjoy the slow freeze that followed as the sun grew dimmer and more distant with every passing day.

Amongst these people were a few who had been preparing for survival almost as soon as Shiva was first detected on the extreme edge of the solar system. The Icelandic government in particular had thrown its every resource into digging deep subterranean shafts and caverns to shelter its populace indefinitely.

Once you knew a few salient facts about the geography and underlying topography of Iceland, the actions of that country’s citizens made perfect sense. Their island home had certain properties that made it ideal for surviving even such a catastrophe: it straddled two continental plates and was dotted with a spectacular number of volcanoes, many of them active.

Like the Iceland of my own alternate, it had long since capitalized on this source of free geothermal energy to heat and power its homes. By the time Shiva loomed in their skies like the harbinger of death it was named after, most of the island’s citizenry had already relocated into the deep artificial caverns – heated and powered by that same geothermal energy.

Unfortunately for them, however, survivors in other parts of the world – mostly military, and mostly in command either of deep underground bunkers or nuclear submarines – decided they wanted those caverns for themselves. Whatever it took. They sailed for Iceland even as the temperatures plummeted, armed with weapons of inconceivable destructive power.

The Icelanders had never stood a chance.