Unafraid, Guilford sat on the crumbling back steps while the others went inside to huddle in the parlor. For a moment he was happily alone, warm enough in his new sweater, the steam of his breath twining up into the breathless radiance of the sky.

Later — in the months, the years, the century of aftermath — countless analogies would be drawn. The Flood, Armageddon, the extinction of the dinosaurs. But the event itself, the terrible knowledge of it and the diffusion of that knowledge across what remained of the human world, lacked parallel or precedent.

In 1877 the astronomer Giovanni Schiaparelli had mapped the canals of Mars. For decades afterward his maps were duplicated and refined and accepted as fact, until better lenses proved the canals were an illusion, unless Mars itself had changed since then: hardly unthinkable, in light of what happened to the Earth. Perhaps something had twined through the solar system like a thread borne on a breath of air, something ephemeral but unthinkably immense, touching the cold worlds of the outer solar system, moving through rock, ice, frozen mantle, lifeless geologies. Changing what it touched. Moving toward the Earth.

The sky had been full of signs and omens. In 1907, the Tunguska fireball. In 1910, Halley’s Comet. Some, like Guilford Law’s mother, thought it was the end of the world. Even then.

The sky that March night was brighter over the northeastern reaches of the Atlantic Ocean than it had been during the Comet’s visit. For hours, the horizon flared with blue and violet light. The light, witnesses said, was like a wall. It fell from the zenith. It divided the waters. It was visible from Khartoum (but in the northern sky) and from Tokyo (faintly, to the west).