Forty-eight hours later, I was back out on another mission, and still in a stinking foul mood.

I looked out and down, seeing rocky coastline half a kilometre below our plane, bordered by a beach that had been turned to fused glass by a thermonuclear detonation. The sun was invisible behind a dense layer of ash in the upper atmosphere that was still decades away from fully precipitating back into the soil.

When I had emerged from the transfer stage just outside this alternate’s version of Phoenix, I had immediately been handed a heavy Arctic-style jacket, and been glad for it. It was freezing cold and would remain so, I was told, for many years yet.

Haden Brooks was in the pilot’s seat, not that he seemed to be doing much piloting. In fact, I had the distinct impression that our aircraft was capable of taking off and landing at its destination without any human intervention whatsoever, although that didn’t prevent him from summoning virtual controls that shimmered into existence around his hands. The plane also lacked anything that looked like an engine and could, he informed me, fly for up to a decade without once refuelling.

Even among as strange and disparate a group as the Pathfinders, Haden Brooks stood out. Apart from his silvered eyes, he was pale enough that he bordered on albino, although his thinning hair was dark and streaked with grey.

‘You ever hear of the Toba eruption?’ asked Haden.

I shook my head. ‘Nope.’

‘It happened about seventy thousand years ago, in all our shared histories,’ he explained. We’d run out of things to say a while back, but clearly Haden was determined to make conversation. ‘It was a hundred times more powerful than Krakatoa, and it nearly wiped out the human race at the time. All that were left were a few thousand survivors, from whom we’re all descended.’

The aircraft bucked slightly as it hit turbulence and I gripped the side of my seat. I wasn’t exactly afraid of flying, but from the outside the aircraft looked about as sturdy as a paper kite.

‘So it was the same as the eruption that did for this alternate?’

‘Pretty much.’

Our debriefing that morning had described how the magma chamber beneath this alternate’s Yellowstone Park had erupted with enormous force, sending thousands of cubic kilometres of ash and sulphur into the atmosphere – much as it had on the alternate on which the Nuyakpuk cousins and their many Inuit relations had managed to survive.

On this alternate, however, a second blow had been dealt by nuclear missiles launched in the immediate aftermath of the eruption. Why they had been launched, and by whom, remained a mystery, but the added radioactive ash in the atmosphere had helped to extend and deepen the global winter to the point where we were pretty sure there were, indeed, no survivors, Inuit or otherwise.