The tree rim was a girdle of fire. Smoke billowed from the ma.s.s of foliage packed into the platform. With cracks like explosions the shaped branches failed and whole sectors of the disc, soaked in flame, came away with great rustles of sparks. Soon only the trunk remained, a gnarled remnant ringed by the stumps of its branches.

At last the disintegrated tree fell away into the sky, and Pallis and Jaen were left, hands still locked, hanging in a void.

The miners were nowhere to be seen.

Pallis looked at Jaen, oddly embarra.s.sed. What, he wondered, should they talk about? "You know, Raft children grow up with a fear of falling," he said. "I guess the flat, steady surface beneath their feet gets taken for granted. They forget that the Raft is no more than a leaf hovering in the air... nothing like as substantial as those huge, impossible planets in that other universe you Scientists tell us about.

"But Belt children grow up on a tatty string of boxes circling a shrunken star. They have no safe plane to stand on. And their fear now wouldn't be of falling, but of having nothing to hang on to..."

Jaen pushed her hair back from her broad face. "Pallis, are you frightened?"

He thought it over. "No. I don't suppose I am. I was more frightened before I kicked the b.l.o.o.d.y fire bowl over."

She shrugged, a mid-air gesture that made her body rock. "I don't seem to be either. I only regret your gamble didn't pay off-"

"Well, it was worth a try."

"-And I'd love to know how it all works out in the end..."

"How long do you think we'll last?"

"Maybe days. We should have brought food pallets. But at least we'll get to see some sights - Pallis!" Her eyes widened with shock; she let go of Pallis's hand and began to make scrambling, swimming motions, as if trying to crawl up through the air.

Pallis, startled, looked down.

The hard surface of a mine sentry craft was flying up toward him; two miners clung to a net cast over the metal. The iron rushed at him like a wallThere was a taste of blood in his mouth.

Pallis opened his eyes. He was on his back, evidently on the mine craft; he could feel the knots of the netting through his shirt. He tried to sit up - and wasn't totally surprised to find his wrists and ankles bound to the net. He relaxed, trying to present no threat.

A broad, bearded face loomed over him. "This one's all right, Jame; he landed on his head."

"Thanks a lot," Pallis snapped. "Where's Jaen?"

"I'm here," she called, out of his sight.

"Are you OK?"

"I would be if these morons would let me sit up."

Pallis laughed - and winced as pain lanced through his mouth and cheeks. Evidently he would have a few new scars to add to his collection. Now a second face appeared, upside down from Pallis's point of view. Palis squinted. "I remember you. I thought I recognized the name. Jame, from the Quartermaster's."

"h.e.l.lo, Pallis," the barman said gloomily.

"Still watering your ale, barman?"

Jame scowled. "You took a h.e.l.l of a chance, tree-pilot. We should have let you drop..."

"But you didn't." Pallis smiled and relaxed.

During the short journey with the miners to the Belt Pallis remembered his wonder on hearing Rees's tale for the first time. In his role as a friend of the returned exile, he had sat with Rees, Decker and Hollerbach in the old Scientist's office, eyes transfixed by the simple hand movements Rees used to emphasize aspects of his adventures.

It was so fantastic, the stuff of legends: the Boneys, the hollow world, the whale, the song... but Rees's tone was dry, factual and utterly convincing, and he had responded to all Hollerbach's questions with poise.

At last Rees reached his description of the whales' great migration. "But of course," Hollerbach breathed. "Hah! It's so obvious." And he banged his old fist into his desk top.

Decker jumped, startled out of his enthrallment. "You silly old fart," he growled. "What's obvious?"

"So many pieces fit into place. Internebular migrations...! Of course; we should have deduced it." Hollerbach got out of his chair and began to pace the room, thumping a bony fist into the palm of his hand.

"Enough histrionics, Scientist," Decker said. "Explain yourself."

"First of all, the whales' songs: these old speculations which our hero has now confirmed. Tell me this: why should the whales have such sizeable brains, such significant intelligence, such sophisticated communication? If you think it through they're basically just grazing creatures, and - by virtue of their sheer size - they are reasonably immune from the attentions of predators, as Rees testifies. Surely they need do little more than cruise through the atmosphere, munching airborne tidbits, needing barely more sense than, say, a tree - avoid this shadow, swim around that gravity well..."

Pallis rubbed the bridge of his nose. "But a tree would never fly into the Core - not by choice anyway. Is that what you're saying?"

"Exactly, tree-pilot. To submit oneself to such a regime of tidal stress and hazardous radiation clearly calls for a higher brain function, a far-sighted imperative to override the more elemental instincts, a high degree of communication - telepathic, perhaps - so that the correct behavior may be instilled in each generation."

Rees smiled. "Also a whale needs to select its trajectory around the Core quite precisely."

"Of course, of course."

Decker's face was a cloud of baffled anger. "Wait... Let's take it one step at a time." He scratched his beard. "What advantage do the whales gain by diving into the Core? Don't they just get trapped down there?"

"Not if they get the trajectory right," said Hollerbach, a little impatiently. "That's the whole point... Do you see? It's a gravitational slingshot." He held up a gaunt fist, mimed rotation by twisting it. "Here's the Core, spinning away. And-" The other hand was held flat; it swooped in toward the Core. "Here comes a whale." The model whale swooped past the Core, not quite touching, its hyperbolic path twisting in the same direction as the Core's rotation. "For a brief interval whale and Core are coupled by gravity. The whale picks up a little of the Core's angular momentum... It actually gains some energy from its encounter with the Core."

Pallis shook his head. "I'm glad I don't have to do that every time I fly a tree."

"It's quite elementary. After all, the whales manage it... And the reason they go through all this is to pick up enough energy to reach the Nebula's escape velocity."

Decker thumped a fist onto the desk top. "Enough of your babbling. What is the relevance of all this?"

Hollerbach sighed; his fingers reached for the bridge of his nose, searching for long-vanished spectacles. "The relevance is this. By reaching escape velocity the whales can leave the Nebula."

"They migrate," Rees said eagerly. "They travel to another nebula... A new one, with plenty of fresh stars, and a blue sky."

"We're talking about a grand transmission of life among the nebulae," Hollerbach said. "No doubt the whales aren't the only species which swim between the clouds... but even if they were they would probably carry across enough spores and seedlings in their digestive systems to allow life to gain a new foothold."

"It's all very exciting." Rees seemed almost intoxicated. "You see, the fact of migration solves another long-standing puzzle: the origin of life here. The Nebula is only a few million shifts old. There simply hasn't been time for life to evolve here in anything like the fashion we understand it did so on Earth."

"And the answer to this puzzle," Hollerbach said, "turns out to be that it probably didn't evolve here after all."

"It migrated to the Nebula from somewhere else?"

"That's right, tree-pilot; from some other, exhausted cloud. And now this Nebula is finished; the whales know it is time to move on. There may have been other nebulae before the predecessor of our Nebula: a whole chain of migrations, reaching back in time as far as we can see."

"It's a marvellous picture," Rees said dreamily. "Once life was established somewhere in this universe it must have radiated out rapidly; perhaps all the nebulae are already populated in some way, with unimaginable species endlessly crossing empty s.p.a.ce-"

Decker stared from one Scientist to the other. He said quietly, "Rees, if you don't come to the point - in simple words, and right now - so help me I'll throw you over the b.l.o.o.d.y Rim with my own bare hands. And the old fart. Got that?"

Rees spread his hands flat on the desk top, and again Pallis saw in his face that new, peculiar certainty. "Decker, the point is - just as the whales can escape the death of the Nebula, so can we."

Decker's frown deepened. "Explain."

"We have two choices." Rees chopped the edge of his hand into the table. "One. We stay here, watch the stars go out, squabble over the remaining sc.r.a.ps of food. Or-" Another chop. "Two. We emulate the whales. We fall around the Core, use the slingshot effect. We migrate to a new nebula."

"And how, precisely, do we do that?"

"I don't, precisely, know," Rees said acidly. "Maybe we cut away the trees, let the Raft fall into the Core."

Pallis tried to imagine that. "How would you keep the crew from being blown off?"

Rees laughed. "I don't know, Pallis. That's just a sketch; I'm sure there are better ways."

Decker sat back, his scarred face a mask of intense concentration.

Hollerbach held up a crooked finger. "Of course you almost made the trip involuntarily, Rees. If you hadn't found a way to deflect that whale, even now you'd be travelling among the star clouds with it."

"Maybe that's the way to do it," Pallis said. "Cut our way into the whales, carry in food and water, and let them take us to our new home."

Rees shook his head. "I don't think that would work, pilot. The interior of a whale isn't designed to support human life."

Once more Pallis struggled with the strange ideas. "So we'll have to take the Raft... but the Raft will lose all its air, won't it, outside the Nebula? So we'll have to build some sort of sh.e.l.l to keep in the atmosphere..."

Hollerbach nodded, evidently pleased. "That's good thinking, Pallis. Maybe we'll make a Scientist of you yet."

"Patronizing old b.u.g.g.e.r," Pallis murmured affectionately.

Again the fire burned in Rees. He turned his intense gaze on Decker. "Decker, somewhere buried in all this bulls.h.i.t is a way for the race to survive. That's what's at stake here. We can do it; have no doubt about that. But we need your support." Rees fell silent.

Pallis held his breath. He sensed that he was at a momentous event, a turning point in the history of his species, and somehow it all hinged on Rees. Pallis studied the young Scientist closely, thought he observed a slight tremble of his cheeks; but Rees's determination showed in his eyes.

At length Decker said quietly, "How do we start?"

Pallis let his breath out slowly; he saw Hollerbach smile, and a kind of victory shone in Rees's eyes; but wisely neither of them exulted in their triumph. Rees said: "First we contact the miners."

Decker exploded: "What?"

"They're humans too, you know," Hollerbach said gently. "They have a right to life."

"And we need them," said Rees. "We're likely to need iron. Lots of it..."

And so Pallis and Jaen had destroyed a tree, and now sat on a Belt rooftop. The star kernel hung above them, a blot in the sky; a cloud of rain drizzled around them, plastering Pallis's hair and beard to his face. Sheen sat facing them, slowly chewing on a slab of meat-sim. Jame was behind her, arms folded. Sheen said slowly, "I'm still not sure why I shouldn't simply kill you."

Pallis grunted, exasperated. "For all your faults, Sheen, I never took you for a fool. Don't you understand the significance of what I've traveled here to tell you?"

Jame smirked. "How are we supposed to know it isn't some kind of trick? Pilot, you forget we're at war."

"A trick? You explain how Rees survived his exile from the Belt - and how he came to ride home on a whale. My G.o.d, his tale comes close to the simplest hypothesis when you think about it."

Jame scratched his dirt-crusted scalp. "The what?"

Jaen smiled. Pallis said, "I'll explain sometime... d.a.m.n it, I'm telling you the time for war is gone, barman. Its justification is gone. Rees has shown us a way out of this gas prison we're in... but we have to work together. Sheen, can't we get out of this b.l.o.o.d.y rain?"

The rain trickled down her tired face. "You're not welcome here. I told you. You're here on sufferance. You're not ent.i.tled to shelter..."

Her words were much as they had been since Pallis had begun describing his mission here - but was her tone a little more uncertain? "Look, Sheen, I'm not asking for a one-way deal. We need your iron, your metal-working skills - but you need food, water, medical supplies. Don't you? And for better or worse the Raft still has a monopoly on the supply machines. Now I can tell you, with the full backing of Decker, the Committee, and whoever b.l.o.o.d.y else you want me to produce, that we're willing to share. If you like we'll allocate you a sector of the Raft with its own set of machines. And in the longer term... we offer the miners life for their children."

Jame leant forward and spat into the rain.

"You're full of c.r.a.p, tree-pilot."

Beside Pallis Jaen bunched a fist. "You b.l.o.o.d.y clod-"

"Oh, shut up, both of you." Sheen pushed wet hair from her eyes. "Look, Pallis; even if I said 'yes' that's not the end of it. We don't have a 'Committee,' or a boss, or any of that. We talk things out among us."

Pallis nodded, hope bursting in his heart. "I understand that." He stared directly into Sheen's brown eyes; he tried to pour his whole being, all their shared memories, into his words. "Sheen, you know me. You know I'm no fool, whatever else I'm guilty of... I'm asking you to trust me. Think it through. Would I have stranded myself here if I wasn't sure of my case? Would I have lost something so precious as-"

Jame sneered. "As what, your worthless life?"

With genuine surprise Pallis turned to the barman. "Jame, I meant my tree."

A complex expression crossed Sheen's face. "Pallis, I don't know. I need time."

Pallis held up his palms. "I understand. Take all the time you want; speak to whoever you want. In the meantime... will you let us stay?"

"You're not stopping at the Quartermaster's, that's for sure."

Pallis smiled serenely. "Barman, if I never sup your dilute p.i.s.s again it will be too soon."

Sheen shook her head. "You don't change, do you, pilot...? You know, even if - if - your story is true, your madcap scheme is full of holes." She pointed to the star kernel. "After working on that thing maybe we have a better feel for gravity than you people. I can tell you, that gravitational slingshot maneuver is going to be b.l.o.o.d.y tricky. You'll have to get it just right..."

"I know. And even as we sit here we're getting some advice on that."

"Advice? Who from?"

Pallis smiled.

Gord woke to a sound of shouting.

He pushed himself upright from his pallet. He wondered vaguely how long he had slept... Here, of course, there was no cycle of shifts, no Belt turning like a clock - nothing to mark the time but sour sleep, dull, undemanding work, foul expeditions to the ovens. Still, the former engineer's stomach told him that at least a few hours had elapsed. He looked to the diminishing pile of food stacked in the corner of his hut - and found himself shuddering. A little more time and perhaps he'd be hungry enough to eat more of the stuff.

The shouting grew in volume and a slow curiosity gathered in him. The world of the Boneys was seamless and incident-free. What could be causing such a disturbance? A whale? But the lookouts usually spotted the great beasts many shifts before their arrival, and no song had been initiated.

Almost reluctantly he got to his feet and made his way to the door.

A crowd of a dozen or so Boneys, adults and children alike, stood on the leather surface of the world with faces upturned. One small child pointed skywards. Puzzled, Gord stepped out to join them.

Air washed down over him, carrying with it a scent of wood and leaves that briefly dispersed the taint of corruption in his nostrils. He looked up and gasped.