Rebka had been making his own inspection. He walked to one of the partitions, and as soon as the twinkling lights had left it he slapped his palm hard against the flat surface. He did the same thing to one of the fine-meshed webs and shook his head.

“Perfectly solid, and strong. We won’t push those aside. If we want to go anywhere, we’ll have to follow the holes in the walls — if we can climb up to them.”

Since their arrival on Glister, Darya had felt increasingly useless. She just didn’t know what to do. Whereas Hans was so used to trouble, he took it all in stride. She could contribute nothing. Unless it was information…

“Hans! What would you say the gravity field is here?”

He stopped his careful inspection of the walls and webs. “A standard gravity, give or take twenty percent. Why? Is it giving you trouble?”

“No. But it’s more than it was, back on the surface. If Glister had a uniform density, or most of the mass was near the outside, then the field would decrease as you went closer to the center. So there has to be a big field source down near the middle. And it can’t be a normal mass; nothing natural is that dense.”

“So it’s something new. Let’s go and take a look below.” Rebka began to walk slowly down one of the corridors, a hallway wide enough for the local vertical to change appreciably across its width.

Darya followed, pausing often to examine the wall materials and the complicated interlocking nets that covered most of the “windows.” Her nervousness disappeared as she realized that this was truly a new Builder artifact — the first one discovered in more than four hundred years. And she was the first scientist ever to examine it. Even if she could escape, she should first give the place the most thorough examination of which she was capable. Otherwise she would never forgive herself — and neither would a thousand other Builder specialists.

So it was panic button off, observation hat on. What else could be said about their surroundings?

Many of the partitions slanted up all the way from floor to glowing ceiling. With their help she could judge the height of the chamber. It was high — maybe sixty meters. Nothing human needed that much space; but it was consistent with the enormous chambers found on other Builder artifacts.

She stepped to one wall and examined the material. Close up, it displayed a fine, grainy structure like baked brick. From the appearance it seemed brittle, as though one sharp blow would shatter it, but she knew from experience with Builder materials that that was an illusion. The structure would possess a material strength beyond anything else in the spiral arm. Left to stand for a million years in a corrosive atmosphere of oxygen, chlorine, or fluorine, it would not crumble. Bathed in boiling acids for centuries, it would not dissolve. Darya had no idea how long this chamber had been unoccupied, but the surfaces should have been as dust-free as if they were polished daily. And they were not. There was dust everywhere.

Maintenance on Glister was sloppily done, if it was done at all.

Darya took the knife from her suit belt and jabbed at the gray wall. The tip was a single crystal of dislocation-free carbon-iridium, the hardest and sharpest material that human technology could create. And yet the blade did not make even a nick. She moved to one of the tight-drawn nets and tried to cut through a thin strand. She could see no mark when she was done. Even the thinnest web would be an impossible barrier to anything that could not, like the cloud, dissolve to small individual components. It was hard to believe that the dust all around them had come from gradual flaking away from the walls. There had to be some other source. Somewhere on Glister there had to be other materials, not built to Builder standards of near-infinite permanence.

Hans Rebka had been waiting impatiently as she chipped at the wall and sawed at the net. “It’ll take you a long time to cut your way out like that,” he said. “Come on. We have to keep moving.”

He did not say what Darya had already thought. The air here might be breathable — though why, and how? There was nothing to create or maintain an atmosphere acceptable to humans — but beyond air, they needed other things to stay alive. Twelve hours had passed since their last meal, and although she was too nervous to feel hungry, Darya’s throat was painfully dry.

They walked on, side by side, taking any floor-level connection between chambers and slowly descending through a long succession of sloping corridors. At last they came to a room containing the first sign of working equipment inside Glister — a massive cylinder that began to hum as they approached. It took in air and blew it out through a series of small vents. Rebka placed his hand and then his face close to one of the apertures.

“It’s an air unit,” he said. “And I think we just started it going. Somehow it reacted to our presence. Here’s something for you to think about: If units like this maintain a breathable atmosphere inside Glister, what does it outside?”

“Probably nothing. There’s nothing up there to do anything, no machinery at all. The surface must be permeable, at least sometimes and somewhere. That’s how we were carried in here. Right through the floor.”

“So all we have to do is work out a way to make the ceilings permeable again, and out we go. Of course, we need a way to jump straight up about a hundred meters.” He stared upward. “The hell with it. I’d still like to know how the unit knew the atmosphere is good enough for both humans and Hymenopts.”

“Right. Or what kind of atmosphere Glister had, before the Have-It-All arrived. Why would it need one, until we got here? Maybe it didn’t have one at all.”

Rebka gave her a startled glance. “Now that’s what I call real custom service. Air designed to order. Now you’re making me nervous.”

They walked on past the air unit and half a dozen other constructs whose purpose Darya could only guess at. She itched to stay and examine them, but Hans was urging her forward.

The eighth device was a waist-high cylinder with a surface like a honeycomb, riddled with hexagonal openings each big enough to accommodate a human fist. The outside of the panel was cold and beaded with drops of moisture. Rebka touched one, sniffed his finger, and touched it to his lips.

“Water. Drinkable, I think, but it tastes flat.”

Darya followed his example. “Distilled. It’s a hundred percent pure, with no salts and minerals. You’re just not used to clean water. You can drink it.”

“Just now I’ll drink anything. But we won’t get much from panel condensation.” He peered into one of the openings. “I’m going to try something. Don’t stand too close.”

“Hans!”

But already he was reaching his arm deep into the aperture. He drew out a cupped handful of water and took a cautious sip. “It’s all right. Come and take some. At least we won’t die of thirst.

“And following up on your earlier line of thought,” he added as they reached in to fill the bottles attached to their suits, “I wonder what liquid that was producing a week ago. Ethanol? Hydrochloric acid?”

“Or liquid methane. What do you think the temperature was on the surface of Glister, when Gargantua was a long way from Mandel?”

They moved on, to reach a point where the uniform curvature of the convex floor was broken by a descending ramp. Rebka stood on the brink and stared down.

“That’s pretty steep. Looks slick, too. More like a chute than a corridor, and I can’t see the bottom. Once we go down there, I’m not sure we’ll be able to climb back up.”

“We need food. We can’t get back to the surface, and we can’t stay here forever.”

“Agreed.” He sat down on the edge. “I’m going to slide. Wait until I call back and tell you it’s all right.”