He was at the equator, where the remnants of the once-global civilization had fled. There were other cities, most in areas that had once been equatorial, some buried in snowfields, still others frozen behind walls of ice.

He and his team knew little yet about the race that had lived here, except that they were a long time dead, and their architecture rivaled anything man had produced. Crystal bridges thrown across mighty rivers, hyperbolic domes, broad walkways in the sky. All frozen now, the bridges as well as the rivers, the crystal as well as the spirit.

It was perhaps a hard irony that Moonlight, which had thrived and died about the time humans were rolling stones out of quarries to build the first pyramids, would probably have remained undiscovered indefinitely had it not been that it was about to receive an unwelcome visitor. A survey ship, the Harry Coker, had been watching an omega, one of the monstrous clouds that drifted in waves out of the galactic core, and which seemed bent on destroying any civilization in their path. The Coker was anxious to see how the cloud would fare in the complex gravity field of a planetary system, when it spotted evidence of cities on the fourth planet.

Collingdale squinted into the hard gray sky. The cloud was visible from late afternoon until shortly after midnight. It was up there now, partially obscured in the glare of the sunset. In the daytime it looked utterly harmless, a large dark thunderstorm, perhaps, like a million others he had seen in his lifetime. But this one rose and set with the sky beyond the atmosphere. It always described the same path across the heavens and it kept getting bigger.

The omega clouds were old news. They’d been discovered a quarter century earlier. Although no one had ever seen them attack a city, they were tied to massive destruction in ancient times on Quraqua, Beta Pacifica III, and two other worlds. Objects with a wide range of geometric shapes had been floated in front of the omegas, and humans now knew beyond any question that designs not found in nature could expect to draw lightning bolts.