It took six hours of steady walking to cross the floor of South Circle, which was less than ten percent of the caldera complex’s total area— all the rest of which was invisible to him for the entire hike. No sign of life, nor of any disturbance to the caldera floor or walls; the atmosphere was visibly thin, everything equally sharp to the eye, right around the primal ten millibars, he judged. The untouched nature of things made him feel uncertain about even his bootprints, and he tried to step on hard rock, and avoid dust patches. It was strangely satisfying to see the primal landscape— quite reddish— though the color was mostly an overlay on dark basalt. His color chart was not good at odd mixes.

Sax had never descended into one of the big calderas before. And even many years spent inside impact craters did not prepare one, he found— for the depth of the chambers, the steepness of the walls, the flatness of the floor. The sheer size of things.

Midafternoon he approached the foot of the northwest arc of the wall. The meeting of wall and floor came up over his horizon, and to his slight relief, the block shelter appeared directly before him; his APS setting had been quite accurate. Not a complicated bit of navigation, but in such an exposed place it was pleasant to be precisely on line. Ever since his experience in the storm so long ago, he had been a bit wary about getting lost. Although there would be no storms up here.

As he approached the hut’s lock doors, a group of people appeared from out of the bottom of a stupendously huge steep gully in the vast broken cliff face, debouching onto the crater floor about a kilometer to the west of the refuge. Four figures, carrying big packs on their backs. Sax stopped, the sound of his breath loud in his helmet: he recognized the last figure immediately. Ann was coming in to resupply. Now he was going to have to think of something to say. And then remember it too.

• • •

Inside the hut Sax unclipped his helmet and took it off, feeling a familiar but most unwelcome tension in his stomach as he did. Every meeting with Ann it got worse. He turned around and waited. Finally Ann came in, and took off her helmet, and saw him. She started as if she were seeing a ghost. “Sax?” she cried.

He nodded. He remembered when they had last met; long ago, on Da Vinci Island; it felt like a previous life. He had lost his tongue.