At 04:47 Coriopolis-standard — still twenty minutes before first simulated light — the air over the Scimitar basin had already begun to turn. It always did. The falls discharge approximately three cubic meters per second from the upper tributary, and at a cylinder rotation of rather less than a revolution per minute the resulting cataract deposits a sustained column of fine mist into a standing low-pressure pocket that the preserve’s environmental-control protocols allow to form unhindered. The pocket settles westward through the night, pulled by the Coriolis deflection that gives the falls their name, and accumulates against the forested ridge on the west bank where it meets cooler air coming off the preserve’s nocturnal temperature curve. By four-thirty, the mist on the west side is dense enough to walk in.

Someone was walking in it. She had come up the trail from the monitoring station an hour before, carrying a thermal-imaging reader and the notebook she still kept by preference, both slung at her hip. She was not monitoring anything this morning. She had set out early because she liked the minute at which the emitters on the inner face of the 2-kilometer gap overhead — eighty kilometers of sky that was not sky — began their transition from the low amber of pre-dawn to a true blue, and she liked to be at the falls for it.

The transition started. Above her, the face of the northern section began to brighten along its spinward curve, the light leading the way rotation turned. At the first suggestion of it, the mist she was standing in lit faintly from above, not yet illuminated so much as aware. The water at the base of the falls, still black, began to trace — because it had been tracing all night, only now visible — the curved descent that, once you saw it, you could not unsee: not a plumb line from lip to basin but a slow sweep sideways, a blade drawn in water. The birds were already up. She had counted seven on the west ridge, and would count more.