Sol was halfway up the sky, a diamond of light. Charon hung directly over Lvov's head, a misty blue disc, six times the size of Luna as seen from Earth. Half the moon's lit hemisphere was turned away from Lvov, towards Sol.

Like Luna, Charon was tidally locked to its parent, and kept the same face to Pluto as it orbited. But, unlike Earth, Pluto was also locked to its twin. Every six days the worlds turned about each other, facing each other constantly, like two waltzers. Pluto-Charon was the only significant system in which both partners were tidally locked.

Charon's surface looked pocked. Lvov had her face plate enhance the image. Many of the gouges were deep and quite regular.

She remarked on this to Cobh, at the Interface.

"The Poole people mostly used Charon material for the building of the wormhole," Cobh said. "Charon is just rock and water-ice. It's easier to get to water-ice, in particular. Charon doesn't have the inconvenience of an atmosphere, or an overlay of nitrogen-ice over the water. And the gravity's shallower."

The wormhole builders had flown out here in a huge, unreliable GUTship. They had lifted ice and rock off Charon, and used it to construct tetrahedra of exotic matter. The tetrahedra had served as Interfaces, the termini of a wormhole. One interface had been left in orbit around Pluto, and the other had been hauled laboriously back to Jupiter by the GUTship, itself replenished with Charon-ice reaction mass.

By such crude means, Michael Poole and his people had opened up the Solar System.

"They made Lethe's own mess of Charon," Lvov said.

She could almost see Cobh's characteristic shrug. So what?

Pluto's surface was geologically complex, here at this point of maximal tidal stress. She flew over ravines and ridges; in places, it looked as if the land had been smashed up with an immense hammer, cracked and fractured. She imagined there was a greater mix, here, of interior material with the surface ice.

In many places she saw gatherings of the peculiar snowflakes she had noticed before. Perhaps they were some form of frosting effect, she wondered. She descended, thinking vaguely of collecting samples.

She killed the scooter's jets some yards above the surface, and let the little craft fall under Pluto's gentle gravity. She hit the ice with a soft collision, but without heat-damaging the surface features much beyond a few feet.

She stepped off the scooter. The ice crunched, and she felt layers compress under her, but the fractured surface supported her weight. She looked up towards Charon. The crimson moon was immense, round, heavy.

She caught a glimmer of light, an arc, directly above her.

It was gone immediately. She closed her eyes and tried to recapture it. A line, slowly curving, like a thread. A web. Suspended between Pluto and Charon.

She looked again, with her face plate set to optimal enhancement. She couldn't recapture the vision.

She didn't say anything to Cobh.

"I was right, by the way," Cobh was saying.