I hurried forward. Turk had already synced himself up with the ship’s interface, and by the frustrated look on his face I could tell he was having trouble working the controls. The wall was still a window; the moon had set; the sky was dark except for the high tip of the Arch, close to zenith now, reflecting a reddish glow that in another couple of hours would be our sunrise.

I put my hand on his shoulder. He looked up and said, “I’ve got a warning display but I don’t know how to read it.”

“Okay. Can you put it into the wall so I can see it too?”

He managed to do that. The display appeared superimposed on the night sky. It was a radar signature with tracking details. Turk said, “It’s seeing something, but I can’t read range or trajectory.”

Were we being chased? But no: the object the ship had detected was high and to the northeast. I said, “The ship pinged us because there shouldn’t be anything in that airspace. Whatever it is, it looks like it’s not on a controlled course. It’s ballistic.”

It was falling, in other words. Probably a natural phenomenon, some piece of ancient debris tumbling out of orbit. But then the alarm chimed and chimed again, and two more targets popped up on the display.

By the end of an hour we had detected five such falling objects, all traveling east to west and roughly parallel to the equator. They were impacting close enough to our charted course that Turk instructed the aircraft to hold and circle until we could figure out what was going on. There was a lull of twenty minutes or so, then the alarm chimed yet again. According to the vector display it had detected an even bigger target this time, maybe big enough to be visible to the naked eye. Turk instructed the ship to aim its window at the appropriate quadrant of the sky.

We looked out into darkness, a few stars beginning to dim behind the first light of the dawn. “There,” Turk said.

The object streaked across the horizon a couple of degrees above the cloud deck. It was as bright as burning phosphorous and it left a luminous trail that quickly faded. The glare of it tracked across the cloudscape and made hectic, moving shadows. Once it had passed out of sight darkness fell again, but only briefly. The next burst of light came from beyond the horizon. That was the impact.

“Ask the ship to calculate its trajectory backward,” I said. “See where it came from.”