“Have you done that?”

“Yes, but it’s too long for me. I usually go out for a week or two.”

“I see.”

It was pretty clear he didn’t.

“We were made to do this, you know,” she said suddenly. “Our bodies are nomads. Humans and hyenas are the two predators that chase their prey down by wearing it out.”

“I like walking,” he allowed.

“So what about you? What do you do to occupy your time?”

“I think,” he said promptly.

“And that’s enough for you?”

He glanced at her. “There’s a lot to think about.”

“But what do you do?”

“I suppose I read. Travel. Listen to music. Look at the visual arts.” He thought some more. “I work on the Titan project, that’s very interesting, I find.”

“And the Saturnian league, more generally, Mqaret tells me. System diplomacy.”

“Yes, well, my name came up in the lottery and I had to do my time, but it’s almost over now, and then I plan to return to Titan and get back to my waldo.”

“So… what were you and Alex working on?”

His pop eyes took on a look of alarm. “Well, some of it she wouldn’t want me to talk about. But she spoke of you often, and now that she’s gone, I just wondered if she might have left you a message. Or even arranged things such that you might be able to step in a bit in her absence.”

“What do you mean?”

“Well, you designed many of the terraria out there, and now they form the bulk of the Mondragon Accord. They would listen to you, perhaps, knowing you were one of Alex’s closest confidantes. So… possibly you could go out with me and meet some people.”

“What, to Saturn?”

“To Jupiter, actually.”

“I don’t want to do that. My life is here, my work. I traveled the system enough when I was young.”

He nodded unhappily. “And… you are quite certain Alex didn’t leave anything for you? Something to give to me, in case something happened to her?”

“Yes, I’m sure! There’s nothing! She didn’t do things like that.”

He shook his head. They sat in silence as the tram slid over the dark face of Mercury. To the north some hilltops were just sparking white with the rising sunlight. Then the top of Terminator’s dome appeared over the horizon, like the shell of a transparent egg. As it cleared the horizon, the city looked like a snow globe, or a ship in a bottle—an ocean liner on a black sea, caught in a bubble of green light. “Tintoretto would have liked your city,” Wahram said. “It looks like a kind of Venice.”

“No it doesn’t,” Swan said crossly, thinking hard.

TERMINATOR

Terminator rolls around Mercury just like its sunwalkers, moving at the speed of the planet’s rotation, gliding over twenty gigantic elevated tracks, which together hold aloft and push west a town quite a bit bigger than Venice. The twenty tracks run around Mercury like a narrow wedding band, keeping near the forty-fifth latitude south, but with wide detours to south and north to avoid the worst of the planet’s long escarpments. The city moves at an average of five kilometers an hour. The sleeves on the underside of the city are fitted over the track at a tolerance so fine that the thermal expansion of the tracks’ austenite stainless steel is always pushing the city west, onto the narrower tracks still in the shade. A little bit of resistance to this movement creates a great deal of the city’s electricity.

From the top of the Dawn Wall, which is a silvery cliff forming the eastern edge of the city, one can see the whole town stretching out to the west, green under its clear dome. The city illuminates the dark landscape around it like a passing lamp; the illumination is very noticeable except at those times when high cliffs west of the city reflect horizontal sunlight into town. Even these mere pinpricks of the dawn more than equal the artificial lights inside the dome. During these cliffblinks nothing has a shadow; space turns strange. Then the mirrors are passed; that light fades. These shifts in illumination are a significant part of the sensation of movement one has in Terminator, for the glide over the tracks is very smooth. Changes in light, slight tilts in pitch, these make it seem as if the town were a ship, sailing over a black ocean with waves so large that when in their troughs, the ship drops into the night, then on high points crests back into day.

The city sliding at its stately pace completes a revolution every 177 days. Round after round, nothing changing but the land itself; and the land only changes because the sunwalkers include landscape artists, who are out there polishing mirror cliffs, carving petroglyphs, erecting cairns and dolmens and inuksuit, and arranging blocks and lines of metal to expose to the melt of day. Thus Terminator’s citizens continuously glide and walk over their world, remaking it day by day into something more expressive of their thoughts. All cities, and all their citizens, move in just such a way.

SWAN AND ALEX

The next day Swan returned to Mqaret’s lab. Again he was in his office staring at nothing. Suddenly Swan realized it was a relief to have something to be angry at.

Mqaret roused himself. “How was your trip out with Wahram?”

“He’s slow, he’s rude, he’s autistic. He’s boring.”

Mqaret smiled a little. “Actually it sounds like you found him interesting.”

“Please.”

“Well, I can assure you Alex found him interesting. She spoke of him pretty often. A few times she made it clear they were involved in things she thought were very important.”

This gave Swan pause, as it was meant to. “Gran, can I have another look around her study?”

“Of course.”

Swan went down the hall to Alex’s room at the end, entered, and closed the door. She went to the one window and looked out at the city, all roof tiles and greenery from this vantage point.

She wandered around the study, looking at things. Mqaret had not yet changed anything. She wondered if he would, and if so, when. All Alex’s things, scattered as always. Her absence was a kind of presence, and again grief stabbed through Swan’s middle and she had to sit down.

After a while she stood and began a more methodical examination. If Alex had left something for her, where would she have put it? Swan could not guess. Alex had wanted always to keep her business offline, out of the cloud, unrecorded, live only, in real time only. But if she had done anything like this, she would have to have figured out some kind of method. Knowing her, it might be a purloined-letter type of thing: a paper note, for instance, right there on her desktop.

So Swan hunted through small stacks of paper on her desk, still thinking it over. If she had had information she wanted Swan to pass along, without Swan necessarily knowing what it was… if there were a lot of data… possibly it would be more than a paper note. And possibly she would want only Swan to find it.

She began to wander the room, talking to herself, and looking closely at things. The room’s control AI would know the room was occupied by only a single person and, with voice and retina, could certainly be set to identify the person.

There was a little toilet room attached to the study, with a sink and mirror, so now she went into it. “I’m here, Alex,” Swan said sadly. “I’m here if you want me.”

She looked into the wall mirror, then into a little oval mirror on a stand next to the sink. Sad Swan’s bloodshot eyes.

A jewelry box next to the oval mirror fell open; Swan jumped back into the wall, then collected herself. She looked in the box. Jewelry tray; take it out; and under it were three small white paper envelopes. All had written on one side In Case of My Death; on the other sides they were marked For Mqaret, For Swan, and For Wang on Io.