And then, just as I was starting to think the rest of my days would be spent negotiating the interminable curve of this stairwell, the steps ended. We came around the final bend to find ourselves looking at a long, softly glowing corridor approximately three metres in height and two in width. For a couple of seconds, we dithered. The stairs had been torture, but the corridor—while seemingly flat and featureless—represented the unknown.

Adam glanced back over his shoulder. “Do you think we can make it to the end before they see us?”

I took him by the wrist. “Well, we can’t stay here.”

Ahead, at the end of the corridor, I could see a black rectangle—an open doorway leading into a darkened area beyond. If we could get to it before the first of our pursuers reached the bottom of the stairs, we could remain hidden—at least, for a few more minutes. We began to run, our legs shaky with hunger and fatigue, our hearts hammering against our ribs, lungs burning.

Adam had a long, loping stride that had been learned and perfected on a treadmill, whereas I was struggling along with ageing leg muscles that had once known military levels of fitness but had since waned in strength and stamina. Only fear and bitter determination kept me moving, my thighs and calves exerting harder than they had been called upon to in years.

As if in a nightmare, the corridor seemed to recede ahead to infinity. We were running but not getting anywhere. My back itched with the anticipation of discovery, cringing against the expectation of bullets…

And then we slammed into the walls at either side of the black doorway.

My chest heaved. Shadows thronged the edge of my vision. My head felt light and I couldn’t catch enough breath to speak. I watched Adam stick his head around the opening, peering into the gloom.

“After you,” he said. He put his arm around my shoulders and I felt the warmth of his chest through the fabric of his shirt. In this sterile alien corridor, it was an absurdly comforting human intimacy.

“It doesn’t look very big.”

“Maybe there’s another door? They wouldn’t have put in all those stairs just to reach a closet.”

I shrugged. The creatures that had built this place had carved an entire solar system into a series of bizarre and undecipherable sculptures. Who knew what other eccentricities they might have indulged in?

Standing on the threshold, I slipped from beneath Adam’s arm and turned to face him. “Look, Adam, I—”

A shout came from the stairs. Two figures stood on the penultimate step, both clad in mismatched and heavily scuffed combat armour and carrying heavy-duty bolt-throwers.

We were caught.

Without a word, Adam shoved me backwards, into the darkness of the small room beyond the door.