A tree rotated in the sky. It was grand and serene, its trunk no more than fifty yards above him.

Gord hadn't seen a tree since his exile from the Belt. Perhaps some of these Boneys had never seen one in their lives.

A man dangled upside down from the trunk, dark, slim and oddly familiar. He was waving. "Gord? Is that you...?"

"Rees? It can't be... You're dead. Aren't you?"

Rees laughed. "They keep telling me I ought to be."

"You survived your jump to the whale?"

"More than that... I made it back to the Raft."

"You're not serious."

"It's a long story. I've travelled from the Raft to see you."

Gord shook his head and spread his hands to indicate the sack of bones that was his world. "If that's true, you're crazy. Why come back?"

Rees called, "Because I need your help..."

13.

ON CLOUDS OF STEAM the plate ship swam toward the Belt. Sheen and Grye stood at the entrance to the Quartermaster's and watched it approach with its cargo of Boneys. Sheen felt dread build up in her, and she shuddered.

She turned to Grye. When the Scientist had first been exiled here by the Raft he had been quite portly, Sheen remembered; now the skin hung from his bones in folds, as if emptied of substance. He caught her studying him. He shifted his drink bowl from hand to hand and dropped his eyes.

Sheen laughed. "I believe you're blushing."

"I'm sorry."

"Look, you've got to lighten up. You're one of us now, remember. Here we are, all humans together, the past behind us. It's a new world. Right?"

He flinched. "I'm sorry..."

"Stop saying that."

"It's just that it's hard to forget the hundreds of shifts we have had to endure since coming here." His voice was mild, but somewhere buried in there was a spark of true bitterness. "Ask Roch if the past is behind us. Ask Cipse." Now Sheen felt her own face redden. Reluctantly she recalled her own hatred for the exiles, how she had willingly allowed their cruel treatment to continue. A hot shame coursed through her. Now that Rees had changed the perspective - given the whole race, it seemed, a new goal - such actions seemed worse than contemptible.

With an effort she forced herself to speak. "If it means anything, I'm sorry."

He didn't reply.

For some moments they stood in awkward silence. Grye's posture softened a little, as if he felt a little more comfortable in her company.

"Well," Sheen said briskly, "at least Jame isn't barring you from the Quartermaster's any more."

"We should be grateful for small mercies." He took a sip from his bowl and sighed. "Not so small, maybe..." He indicated the approaching plate. "You miners do seem to have accepted us a lot more easily since the first Boneys arrived."

"I can understand that. Perhaps the presence of the Boneys shows the rest of us how much we have in common."

"Yes."

The Belt's rotation carried the Quartermaster's beneath the approaching plate once again. Sheen could see that the little craft carried three Boneys, two men and a woman. They were all squat and broad, and they wore battered tunics provided by the Belt folk. Sheen had heard legends of what they chose to wear on their home worldlet... She found herself shuddering again.

The Belt was being used as a way station between the Bone world and the Raft; Boneys traveling to the Raft would stay here for a few shifts before departing on a supply tree. At any one time there was, Sheen reminded herself, only a handful of Boneys scattered around the Belt... but most miners felt that handful was too many.

The Boneys stared down at her, thick jaws gaping. One of the men caught Sheen's eye. He winked at her and rolled his hips suggestively. She found her food rising to her throat; but she held his stare until the plate had pa.s.sed over the Belt's narrow horizon. "I wish I could believe we need those people," she muttered.

Grye shrugged. "They are human beings. And, according to Rees, they didn't choose the way they live. They have just tried to survive, as we all must do... Anyway, we might not need them. Our work with the Moles on the star kernel is proceeding well."

"Really?"

Grye leaned closer, more confident now that the conversation had moved onto a topic he knew about. "You understand what we're trying to do down there?"

"Vaguely..."

"You see, if Rees's gravitational slingshot idea is going to work we will have to drop the Raft onto a precise trajectory around the Core. The asymptotic direction is highly sensitive to the initial conditions-"

She held up her hands. "You'd better stick to words of one syllable. Or less."

"I'm sorry. We're going into a tight orbit, very close to the Core. The closer we pa.s.s, the more our path will be twisted around the Core. But the differences for a small deviation are dramatic. You have to imagine a pencil of neighboring trajectories approaching the Core. As they round the singularity they fan out, like unraveling fibers; and so a small error could give the Raft a final direction very different from the one we want."

"I understand... I think. But it doesn't make much difference, surely? You're aiming at a whole nebula, a target thousands of miles wide."

"Yes, but it's a long way away. It's quite a precise piece of marksmanship. And if we miss, by even a few miles, we could end up sailing into empty, airless s.p.a.ce, on without end..."

"So how is the Mole helping?"

"What we need to do is work out all the trajectories in that pencil, so we can figure out how to approach the Core. It takes us hours to work the results by hand - work which, apparently, was performed by slavelike machines for the original Crew. It was Rees who had the idea of using the Mole brains."

Sheen pulled a face. "It would be."

"He argued that the Moles must once have been flying machines. And if you look closely you can see where the rockets, fins and so on must have fitted. So, argued Rees, the Moles must understand orbital dynamics, to some extent. We tried putting our problems to a Mole. It took hours of question-and-answer down there on the kernel surface... but at last we started getting usable results. Now the Mole provides concise answers, and we're proceeding quickly."

She nodded, juggling her drink. "Impressive. And you're sure of the quality of the results?"

He seemed to bridle a little. "As sure as we can be. We've checked samples against hand calculations. But none of us are experts in this particular field." His voice hardened again. "Our Chief Navigator was Cipse, you see."

She could think of no reply. She drained the last of her globe. "Well, look, Grye, I think it's time I-"

"Now, then, where can old Quid take a drink around here?"

The voice was low and sly. She turned, startled, and found herself looking down at a wide, wrinkled face; a grin revealed rotten stumps of teeth, and black eyes traveled over her body. She couldn't help but shrink away from the Boney. Vaguely she was aware of Grye quailing beside her. "What... do you want?"

The Boney stroked a finely carved spear of bone. His eyes widened in mock surprise. "Why, darling, I've only just arrived, and what kind of welcome is that? Eh? Now that we're all friends together..." He took a step closer. "You'll like old Quid when you get to know him-"

She stood her ground and let her disgust show in her face. "You come any nearer to me and I'll break your b.l.o.o.d.y arm."

He laughed evenly. "I'd be interested to see you try, darling. Remember I grew to my fine stature in high-gee... not this baby-soft micro gravity you have here. You're muscled very attractively; but I bet your bones are as brittle as dead leaves." He looked at her acutely. "Surprised to find old Quid using phrases like 'micro gravity,' girl? I may be a Boney, but I'm not a monster; nor am I stupid." He reached out and grabbed her forearm. His grip was like iron. "It's a lesson you evidently need to learn-"

She thrust at the wall of the Quartermaster's with both legs and performed a fast back flip, shaking free his hand. When she landed she had a knife in her fist.

He held up his hands with an admiring grin. "All right, all right..." Now Quid turned his gaze on Grye; the Scientist clutched his drink globe to his chest, trembling. "I heard what you were saying," Quid said. "All that stuff about orbits and trajectories... But you won't make it, you know."

Grye's cheeks quivered and stretched. "What do you mean?"

"What are you going to do when you're riding your bit of iron, down there by the Core himself - and you find you're on a path that isn't in your tables of numbers? At the critical moment - at closest approach - you'll have maybe minutes to react. What will you do? Turn back and draw some more curves on paper? Eh?"

Sheen snorted. "You're an expert, are you?"

He smiled. "At last you're recognizing my worth, darling." He tapped his head. "Listen to me. There's more on orbits locked in here than on all the bits of paper in the Nebula."

"Rubbish," she spat.

"Yes? Your little friend Rees doesn't think so, does he?" He hefted his spear in his right hand; Sheen kept her eyes on the spear's bone tip. "But then," Quid went on, "Rees has seen what we can do with these things-"

Abruptly he twisted so that he faced the star kernel; with surprising grace he hurled the spear. The weapon accelerated into the five-gee gravity well of the kernel. Moving so fast that it streaked in Sheen's vision, it missed the iron horizon by mere yards and twisted behind the star-and now it emerged from the other side of the kernel, exploding at her like a fist. She ducked, grabbing for Grye; but the spear pa.s.sed a few yards above her head and sailed away into the air.

Quid sighed. "Not quite true. Old Quid needs to get his eye in. Still-" He winked. "Not bad for a first try, eh?" He prodded Grye's sagging paunch. "Now, that's what I call orbital dynamics. And all in old Quid's head. Astonishing, isn't it? And that's why you need the Boneys. Now then, Quid needs his drink. See you later, darling..."

And he brushed past them and entered the Quartermaster's.

Gord shoved his thinning blond hair from his eyes and thumped the table. "It can't be done. I know what I'm talking about, d.a.m.n it."

Jaen towered over the little engineer. "And I'm telling you you're wrong."

"Child, I've more experience than you will ever-"

"Experience?" She laughed. "Your experience with the Boneys has softened your brains."

Now Gord stood. "Why, you-"

"Stop, stop." Tiredly Hollerbach placed his age-spotted hands on the table top.

Jaen simmered. "But he won't listen."

"Jaen. Shut up."

"But - ah, d.a.m.n it." She subsided.

Hollerbach let his eyes roam around the cool, perfect lines of the Bridge's Observation Room. The floor was covered with tables and spread-out diagrams: Scientists and others pored over sketches of orbital paths, models of grandiose protective sh.e.l.ls to be built around the Raft, tables showing rates of food consumption and oxygen exhaustion under various regimes of rationing. The air was filled with feverish, urgent conversation. Wistfully Hollerbach recalled the studied calm of the place when he had first joined the great Cla.s.s of Scientists; in those days there had still been some blue in the sky, and there had seemed all the time in the world for him to study...

At least, he reflected, all this urgent effort was in the right direction, and seemed to be producing the results they needed to carry through this scheme. The tables and dry graphs told a slowly emerging tale of a modified Raft hurtling on a courageous trajectory around the Core; these sober Scientists and their a.s.sistants were together engaged on man's most ambitious project since the building of the Raft itself.

But now Gord had walked in with his sc.r.a.ps of paper and his pencil jottings... and his devastating news. Hollerbach forced his attention back to Gord and Jaen, who still confronted each other - and he found his eyes meeting Decker's. The Raft's leader stood impa.s.sively before the table, his scarred face clouded by a scowl of concentration.

Hollerbach sighed inwardly. Trust Decker, with his instinct for the vital, to arrive at the point of crisis. "Let's go through it again, please, engineer," he said to Gord. "And this time, Jaen, try to be rational. Yes? Insults help n.o.body."

Jaen glowered, her broad face crimson.

"Scientist, I am - was - the Belt's chief engineer," Gord began. "I know more than I care to remember about the behavior of metals under extreme conditions. I've seen it flow like plastic, turn brittle as old wood..."

"No one is questioning your credentials, Gord," Hollerbach said, unable to contain his irritation. "Get to the point."

Gord tapped his papers with his fingertips. "I've studied the tidal stresses the Raft will undergo at closest approach. And I've considered the speeds it must attain after the slingshot, if it's to escape the Nebula. And I can tell you, Hollerbach, you haven't a hope in h.e.l.l. It's all here; you can check it out-"

Hollerbach waved his hand. "We will, we will. Just tell us."

"First of all, the tides. Scientist, the stresses will rip this Raft to pieces, long before you get to closest approach. And the fancy structures your bright kids are planning to erect over the deck will simply blow apart like a pile of twigs."

"Gord, I don't accept that," Jaen burst out. "If we reconfigure the Raft, perhaps b.u.t.tress some sections, make sure our att.i.tude is correct at closest approach-"

Gord returned her gaze and said nothing.

"Check his figures later, Jaen," Hollerbach said. "Go on, engineer."

"Also, what about air resistance? At the speeds required, down there in the thickest air of the whole Nebula, whatever shoal of fragments emerges from closest approach is simply going to burn up like so many meteors. You'll achieve a spectacular fireworks display and little more. Look, I'm sorry this is so disappointing, but your scheme simply cannot work. The laws of physics are telling you that, not me..."

Decker leaned forward. "Miner," he said softly, "if what you say is true then we may after all be doomed to a slow death in this stinking place. Now, maybe I'm a poor judge of people, but you don't seem too distressed by the prospect. Do you have an alternative suggestion?"

A slow smile spread over Gord's face. "Well, as it happens..."

Hollerbach sat back, letting his jaw drop. "Why the h.e.l.l didn't you tell us in the first place?"

Gord's grin widened. "If you'd troubled to ask-"

Decker laid a ma.s.sive hand on the table. "No more word games," he said quietly. "Miner, get on with it."

Gord's grin evaporated; shadows of fear chased across his face, reminding Hollerbach uncomfortably of how much this blameless little man had endured. "n.o.body's threatening you," he said. "Just show us."

Looking more comfortable, Gord stood and led them out of the Bridge. Soon the four of them - Gord, Hollerbach, Decker and Jaen - stood beside the dull glow of the Bridge's hull; the starlight beat down, causing beads of perspiration to erupt over Hollerbach's bald scalp. Gord stroked the hull with his palm. "When was the last time you touched this stuff? Perhaps you walk past it every day, taking it for granted; but when you come at it fresh, it's quite a revelation."

Hollerbach pressed his hand to the silver surface, feeling his skin glide smoothly over it... "It's frictionless. Yes. Of course."

"You tell me this was once a vessel in its own right, before it was incorporated into the deck of the Raft," Gord went on. "I agree with you. And furthermore, I think this little ship was designed to travel through the air."

"Frictionless," Hollerbach breathed again, still rubbing his palm over the strange metal. "Of course. How could we all have been so stupid? You see," he told Decker, "this surface is so smooth the air will simply slide over it, no matter what speed it travels. And it won't heat up as would ordinary metal...

"And no doubt this structure would be strong enough to survive the tidal stresses close to the Core; far better, at least, than our ramshackle covered Raft. Decker, obviously we'll have to go through Gord's calculations, but I think we'll find he's correct. Do you see what this means?" Something like wonder coursed through Hollerbach's old brain. "We'll have no need to build an iron bell to keep our air in place. We can simply close the Bridge port. We will ride a ship as our ancestors rode... Why, we can even use our instruments to study the Core as we pa.s.s. Decker, a door has closed; but another has opened. Do you understand?"

Decker's face was a dark mask. "Oh, I understand, Hollerbach. But there's another point you might have missed."