The hat’s brim was piled with pleats of fine material, knotted into place by ties fixed through holes in the leather of the hat. Mur imagined undoing those ties; perhaps a kind of net would drop down, around the head.

“It’s odd, but what about it?”

“Remember Dura’s tales of her time on the ceiling-farm. The Air-tanks they made her wear, working high up, close to the Crust. The masks…”

“Oh. Right.” Mur nodded. “Those hats must have come from coolies’ Air-tanks.”

“So my guess is these people used to be coolies. Maybe they ran away.”

“But they ought to know about Parz.”

Philas laughed without humor. She seemed in control of herself again, but her mood was black. “So they are concealing things from us. Well, we lied to them. That’s what the world is like, it seems.”

Mur stared at Borz’s hat. Apart from Deni Maxx’s Air-car it was the first artifact even remotely related to the City he’d ever seen. And recognizing it now from Dura’s description somehow lent veracity to Dura’s bizarre tale. He felt oddly reassured by the confirmation of this small detail, as if somewhere inwardly he’d imagined Dura might be lying, or mad.

The people turned to stare, suspicious and hostile, as the Human Beings were brought into the encampment by Borz and his companion. There seemed to be around forty humans in the little colony, perhaps fifteen of them children and infants. The adults were fixing clothes, mending nets, sharpening knives, lounging in the Air and talking. Children wriggled around them like tiny rays, their bare skins crackling with electron gas. None of it would have looked out of place in any of the Human Beings’ encampments, Mur thought.

The tetrahedral artifact loomed beyond the small-scale human activities. It was a skeletal framework, incongruous, sharp, dark.

Borz and the woman hung back as Mur and Philas hesitantly approached the tetrahedron’s forbidding geometries. Mur peered up at the framework. The edges were poles a little thicker than his wrist, each about ten mansheights long. They were precisely machined of some dull, dark substance. The four triangular faces defined by the edges enclosed nothing but ordinary Air — in fact, the people here had slung sections of net to enclose a small herd of squabbling, starved-looking Air-pigs at the framework’s geometric center. Elsewhere on the framework rough bags had been fixed by bits of rope; irregular bulges told Mur that the bags probably contained food, clothes and tools.

Mur moved forward, reached out a tentative hand and laid his palm against one edge. The material was smooth, hard and cold to the touch. Maybe this was the Corestuff of which Dura had spoken, extracted from the forbidding depths of the underMantle by City folk (and now, unimaginably, by the boy Farr whom Mur had grown up with).

Philas asked, “Can we go inside?”

The woman laughed. “Of course you can. Your friend was right… nothing works, any more.”

The man grunted to Mur. “We’d hardly keep our pigs in there if they were going to be whisked off to the North Pole at any moment.”

“I imagine not.”

Philas passed cautiously through one face of the tetrahedron. Mur saw her shiver as she crossed the invisible plane marked by the edges. She hovered close to the pigs and turned in the Air, peering into the corners of the tetrahedron.

The man — Borz — grunted. “Oh, what the hell.” He dug into one of the bags dangling on the tetrahedral frame and extracted a handful of food. “Here.”

Mur grabbed the food. It was stale, slightly stinking Air-pig flesh. Mur allowed himself one deep bite before stuffing the rest into his belt. “Thank you,” he said around the mouthful of food. “I can see you’ve little to spare.”

The woman drifted closer to him. “Once,” she said slowly, “this frame sparkled blue-white. As if it was made of vortex lines. Can you imagine it? And it really was a wormhole Interface; you could pass through it and cross the Mantle in a heartbeat.” For a moment she sounded sad — nostalgic for days she’d never seen — but now her dismissive expression returned. “So they say, anyway. But then the Core Wars came…”

After raising several generations of Human Beings, the Colonists had suddenly withdrawn. According to the Human Beings’ fragmented oral histories the Colonists had retreated into the Core, taking most of the marvelous Ur-human technology with them, and destroying anything they were forced to leave behind.

The Human Beings had been left stranded in the Air, helpless, with no tools save their bare hands.

Perhaps the Colonists had expected the Human Beings to die off, Mur wondered. But they hadn’t. Indeed, if Dura’s tales of Parz and its hinterland were accurate, they had begun to construct a new society of their own, using nothing but their own ingenuity and the resources of the Star. A civilization which — if not yet Mantle-wide — was at least on a scale to bear comparison with the great days of the ancients.

“The wormholes collapsed,” the woman said. “Most of the Interfaces were taken away into the Core. But some of them were left behind, like this one. But its vortex-light died. Now it just drifts around in the Magfield…”

“I wonder what happened to the people inside the wormholes,” Mur said. “When the holes collapsed.”

Philas came drifting out of the tetrahedron. “Come on, Mur,” she said tiredly.

Mur thanked Borz for the scrap of food, and nodded to the woman — whose name, he realized, he’d never learned.

The pair barely reacted, and their scowls seemed to be returning. Their spears had never left their hands, Mur noticed.

They Waved out of the little encampment. A child jeered at them, until silenced by a parent; Mur and Philas didn’t look back.

They began to Wave upward, side by side.

Mur gazed up at the Crust-forest. “That seems a hell of a long way back,” he said. “To have come all this way, for a handful of meat…”

“Yes,” Philas said savagely, “but we might have found riches. Riches beyond imagining. We had to come.”

“I wonder why they stay here, close to the Interface. Do you think it protects them, when Glitches come?”

“I doubt it,” Philas said. “After all, the thing floats freely, they said. It’s just a relic, a ruin from the past.”

“Then why do they stay?”

“For the same reason Dura’s City folk built their City at the Pole.” Philas waved her hands at the empty Mantlescape, the arching vortex lines. “Because it’s a fixed point, in all this emptiness. Something to cling to, to call home.” She wiped her eyes with the back of her hand; already she seemed short of breath. “Better than drifting, like we do. Better than that.”

Mur lifted his face to the Crust-forest and Waved hard, ignoring the gathering ache in his hips, knees and ankles.

Dura made sure it was she, not Farr, whom Hork chose to go on the journey into the underMantle.

At first Adda tried to explain Dura’s reasoning to Farr, to provide a bridge between them; but he could see that Farr was devastated. The boy mooched around the Upside apartment Hork had loaned the Human Beings like a trapped Air-pig. Adda wistfully watched him prowl, recalling Logue as a young man. The underMantle journey had many potent elements for Farr — the chance to protect his sibling by taking her place, the intrinsic excitement of the jaunt itself. Farr was still such a melange of boy and man.

But — if one of the three Human Beings must go on this absurd trip — then Dura was the best choice. Farr didn’t have the maturity, or Adda himself the strength, to cope with the challenges the journey would provide…

Adda cursed himself silently. Even in the privacy of his own mind he was starting to use the diluted language of the City folk, to be influenced by their gray thinking. Into the Core with that.