She had done her bit on the shield. She should have stayed retired, she thought wistfully.

And it was when Edna came on line with her bit of bad, strange news that it was driven home to Bella that she really was the commander-in-chief of a space navy.

“For once the trackers think they’ve found something serious, Mum. Something out in the dark — now approaching the orbit of Jupiter, in fact, and falling in on a hyperbolic trajectory. It’s not on the Extirpator map, though that’s not so unusual; long-period comets too remote for Extirpator echoes are turning up all the time.

This thing has other characteristics that are causing them concern…”

Bella had seen a rendering of the “Extirpator map,” set up like a planetarium inside her own base, the old NASA headquarters building in Washington. An immense, dynamic, three-dimensional snapshot of the whole of the solar system, it had been created on the very eve of the sunstorm by the deep-space explosion of a ferocious old nuke called the Extirpator — a detonation that had also broadcast to the silent stars a wistful concatenation of human culture called “Earthmail,” within which were embedded copies of the planet’s greatest artificial minds, called Aristotle, Thales, and Athena. Within a few hours of the explosion the radio telescopes on Earth had logged X-ray echoes of the blast coming back from every object larger than a meter across inside the orbit of Saturn.

Twenty-seven years after the sunstorm the human worlds and space itself were full of eyes, tracking anything that moved. Anything not shown in the map must be a new entrant. Most newcomers, human or natural, could be identified and eliminated quickly.

And if not — well, then, Bella was learning, the bad news quickly filtered up the Council’s hierarchy to her own ears.