“I think so.” His eyes were fixed on nothing. “It’s the Witch in the Well, Geena. The demon at the heart of the Moon.”

“But what is it? Some geological thing?”

“No…”

He told her his hypothesis.

It came to Earth when the Solar System was young.

One day, human scientists would call it the Impactor.

It had about the mass of Mars, a tenth of Earth’s. Humans would later speculate that it was a young planet in its own right.

But they were wrong. It was not a planet.

Its heart was a dense block of matter, complex, its surface shifting, silvery. It was a hundred miles across, extraordinarily dense.

This core came trailing a cloud of silvery motes. Where the motes touched, worldlets were transformed. Raw materials rained down on the surface of the core.

It was heading for the sun. There, less than a solar radius from the young sun’s roiling surface, a great sail would be unfurled — or rather assembled, from the materials leached from the young Solar System. The sail would be almost perfectly reflective, so much so that it would have been cool, to a human touch. Humans would one day speculate about such objects, as designs for craft to cross the gulfs between the stars.

But this was no craft. To a human eye, the sail would have looked organic, its surface as structured — and as beautiful — as a young leaf.

The flood of raw sunlight would hurl the core, the sail and its attendant cloud out of the Solar System, and on to a new destination, another young system, pregnant with resources.

Perhaps that was the plan. Or perhaps the intention was different. Or perhaps there was no conscious intention.

From without, it was impossible to say.

Whatever its purpose, the object barrelled through the dusty plane of the Solar System, heading for the sun.

But there seemed to be something in the way.

“Earth,” Geena said. “You’re saying the Moonseed hive — ship, whatever — was the Impactor which hit the Earth—”

“And created the Moon. And it’s still here, deep inside the Moon.” He laughed. “Ironic, isn’t it? Without that impact — without the Moonseed — life on Earth wouldn’t even exist. But now it’s going to destroy us.”

She studied him. “Let me summarize. A massive Moonseed hive crashes into the Earth. The impact forms the Moon. The hive becomes trapped at the core of the Moon. Its cloud of, umm, nano manufacturer insects, is trapped in the Moon’s fabric. They stop their destructive behaviour because of some kind of asimov inhibitor… It sounds like something your dippy girlfriend would come up with.”

“Jane’s too sensible for this stuff. Look, it’s a consistent hypothesis. This mass concentration at the heart of the Moon, the wreckage, is actually a confirmation.”

She said, “But what about Venus? All that stuff about a black hole rocket—”