'I will talk to people I know in Tank Town,' Avernus said. 'They will remotely pilot an aeroshell into orbit and I will ride it down to a place where I can meet and talk with Professor Doctor Hong-Owen.'

'She wants to take you prisoner,' Macy said. 'I don't think you'll be able to change her mind.'

'Do you believe in serendipity?' Avernus said.

'If I knew what it was I could tell you,' Newt said.

'The lucky accident,' Macy said.

'It means that we can talk on my terms,' Avernus said. 'On Titan.'

She was adamant that she would ride down to Titan alone, and her logic was impregnable. Elephant could not outrun their pursuers, so they must set down somewhere. Two of the moons they could reach before the Uakti caught up with them, Atlas and Helen, were too small to provide any real hiding place, and there was a Brazilian ship in orbit around the third, Rhea. So Titan was the only real choice. But Elephant could not land on Titan, and it would be a very bad idea to abandon her in orbit. And since it was clear that Sri Hong-Owen was interested only in her, Avernus said, it was right and proper that she should not put Macy and Newt's lives at risk. So she would ride down to Titan and deal with her pursuer, and Macy and Newt would be free to travel on to Uranus. Macy and Newt tried to argue with her, but the gene wizard insisted that there was no other acceptable course of action. Either she went down to the surface of Titan alone, or she would stay aboard Elephant, and they would all be captured.

'I've heard more than a few rumours about your work down there,'

Newt said. 'Would any of them happen to be true?'

'I don't listen to rumours,' Avernus said.

'You have a surprise planned,' Newt said. 'I know you do.'

'You're enjoying this,' Macy told him.

'It isn't one of your ordinary days, that's for sure.'

They crossed the narrow ringlets at the inner edge of the ring system and skimmed in low around Saturn's banded cloudscape. As soon as the pursuing ship dropped beneath the horizon, Macy felt a jerky vibration as attitude jets fired. Then Saturn's gravity gripped the ship and flung it outwards like a stone swung on a string, the exchange of momentum boosting their velocity by more than fifty per cent while slowing the gas giant's rotation by considerably less than a yoctosecond.

Usually, they would head towards Titan or any of the other moons using the ancient fuel-saving free-return system, with Saturn's gravity slowing them as they fell outwards so that by the time they reached Titan they would be travelling at roughly its orbital velocity, and only a small correction burn would be required to nudge them into orbit. But Newt kept the motor lit so that they could stay ahead of their pursuers, and he would have to keep it burning until Elephant reached the point where it would have to turn around to decelerate, or else fly past Titan at too high a velocity to be captured by the moon's gravity.

Elephant shot through the Cassini Division, out of shadow into sunlight, angling towards Titan. It had passed beyond the outer edge of the main ring system when the Brazilian shuttle came around the edge of Saturn. Its motor was still lit and it was heading out on the same course as Elephant. Newt's attempt to hoodwink them hadn't worked. Either they'd made a one-in-a million guess or, more likely, someone had fed them information about the course correction during Elephant's transit.

'It cuts our margin to the bone,' Newt said. 'They'll arrive in orbit around Titan just seventy-nine minutes after we do.'

'It's time I talked to the people in Tank Town,' Avernus said. 'If they put the aeroshell in orbit now, will you be able to rendezvous with it before the Uakti can catch up with us?'

'It won't be a problem as long as they put it where I tell them to put it,'

Newt said.

He and Avernus had a long conversation with Titan's traffic control. When they'd finished, Macy said to the gene wizard, 'If we knew what you were planning to do, we might be able to help you.'

'It's simply a question of getting them to land where I want them to land,' Avernus said, and wouldn't say anything else.

Hours passed. The system's net was down, but Newt was able to tune into broadcasts from Iapetus and the inner moons and in this manner they learned about Paris's final fall, the fierce fighting around Athens and Spartica on Tethys, and the formal surrender of Baghdad, Enceladus. There was a remarkably calm eyewitness account of an attempt by two tugs to ram the Flower of the Forest, one shredded by kinetic weapons, the other cut down by a singleship. Reports of squads of Pacific Community soldiers securing the scattered farming communities on Iapetus. Yet all of this deadly and frenetic activity was lost in the majestic and serene panorama of Saturn and its rings, slowly dwindling behind Elephant. Against that vast and inhuman backdrop the war was as insignificant as the struggle between a couple of handfuls of microbes in the unchained waters of an ocean.

At last, Newt switched off Elephant's motor, turned the tug around, and fired up the motor again. They had to slow down now, match Titan's orbital velocity. Their pursuer kept coming. Drawing closer and closer because it was still accelerating.

Macy had the Uakti's bright star centred in the widescreen view in the memo space. Readouts showed the steady decrease in the distance between Elephant and the shuttle, and the steady increase in the shuttle's relative velocity. Her anxiety and dismay swelled. If they'd guessed wrong about the Uakti's intentions, it might well continue to accelerate, overhaul Elephant and cripple it with judicious use of a kinetic weapon or a proxy, then circle around Titan and come back and claim its prize. The gap between the two ships narrowed to thirty thousand kilometres and continued to close, but at a much slower rate now. After a moment, Macy realised that the Uakti had switched off its fusion motor. She saw a brief twinkling flash as it fired its attitude jets and turned end for end, and then its fusion motor flamed on again, a star brighter than the shrunken disc of the sun. Still it continued to creep towards Elephant, both ships falling now at the same rate towards Titan's foggy crescent.

The dreamers of the early space age had suggested that Titan would be a vast resource of hydrocarbons and nitrogen, but it had turned out to be much easier to mine CHON from carbonaceous chondrite deposits on Iapetus and the inner moons than scoop it from Titan's atmosphere, and the moon's freezing shroud of smoggy haze and its relatively steep gravity well made it about as appealing a piece of real estate as an outer suburb of Hell. Few Outers had chosen to live there: a sprinkling of hermitages and oases, and the anarchist collective of Tank Town, on the shore of the Lunine Sea, which tinkered with bizarre vacuum organisms and manufactured exotic plastics and other organic chemicals. No more than five hundred souls in all, scattered across a moon with a diameter of more than five thousand kilometres, larger than Mercury. So far it had not been touched by the war.

Elephant swung into orbit around Titan's equator and there was a tiny star dead ahead: the aeroshell sent up by remote control by traffic control in Tank Town. It was a measure of Avernus's reputation that the Tank Towners would commit one of their craft on such a risky venture. They'd gain an immense amount of kudos for it, of course, but who knew what that would be worth, now that the three great powers from Earth were on the brink of taking control of the Saturn System? Yet there it was, growing from a point of light to a clamshell capsule bright and sharp against Titan's ochre cloudscape. Newt had calculated the orbital trajectories of Elephant and the aeroshell so precisely that they were already drawing alongside, Elephant shuddering delicately as attitude jets adjusted her pitch. Macy felt a forceful surge of pride at his skill.

Avernus had by this time climbed into her pressure suit and was waiting in the airlock. Now, with only a cursory farewell, she cycled through and kicked off and shot across the thirty-metre gap, catching a recessed handhold beside the open hatch and swinging neatly inside.

'More than two hundred years old, and spry as a monkey,' Newt said.

'She's sending a message to Sri Hong-Owen, telling her where to meet up. Want to listen in?'

Macy listened to the brief message and said, 'She's probably the most intelligent person I ever met. A genuine, certified genius. The problem is, she doesn't know anything about people.'

'Too right.'

'So we aren't going to leave her behind, are we?'

'I have a couple of good friends in Tank Town,' Newt said. 'Flying buddies. Let me talk to them and see if we can come to a deal. Meanwhile, I think I should widen our orbit a little, make it at least look like we're running off.'

In the memo space's widescreen view, the chemical motor of the aeroshell flared, slowing the little craft and taking it out of orbit, down to Titan's surface.

12.

Titan was similar in size to Ganymede and Callisto, but while the two Jovian moons had long ago lost their primordial atmospheres frigid Titan was shrouded in a dense envelope of nitrogen and methane, and an opaque orange haze of photochemical smog. Hydrocarbon grains formed by the action of ultraviolet light on methane in the upper reaches of the atmosphere drifted down to the surface and formed gritty black aggregates that in the equatorial regions were swept and sculpted by winds into vast seas of dunes a hundred metres high and running in parallel rows for hundreds of kilometres. Methane and ethane rains filled lakes and seas and fed rivers that carved ramifying channels through water-ice highlands and flooded across lowland basins.

As the Uakti powered towards the rendezvous point under a sky sheeted from horizon to horizon with orange haze, Sri was surprised at how familiar the landscape seemed. They were flying north above what was clearly a volcanic range, domes and complex calderas strung across broad, dark outflow slopes dissected by brighter channels and fissures and collapse depressions. The largest of the collapse depressions were flooded with liquid methane and ethane that gleamed like spills of oil in the dull even light.

The Uakti glided towards a volcanic pancake dome crowned by a caldera whose slumped rim circled a shallow basin some ten kilometres across and floored with black water-ice. A craggy secondary cone, a volcano within a volcano, was offset inside the caldera like the pupil of an eye glancing sideways. A bright green beacon pulsed near the dished top of the secondary cone, marking the position of a landing platform. A small dome sat on a cutback terrace beyond.

All this glimpsed in a moment, and then the shuttle swept past and made a wide turn to come back again, and Yamil Cho presented Sri with data from radar, microwave, and multiband imaging. The water-ice lava that had flooded the caldera formed a solid plug averaging more than sixty metres deep, with a dyke of liquid water beneath. Treelike vacuum organisms thickly covered the slopes of the secondary cone and the inner slopes of the caldera, but stopped short of the caldera's floor, presumably because it was significantly warmer and therefore deadly to organisms growing at the ambient temperature of -180 Centigrade. The dome set high on the secondary cone was pressurised but appeared to be deserted. Three kilometres east, more or less in the centre of the caldera, a single figure stood on a ridge above the hot spot of a small, active vent.

'She kept her promise,' Sri said.

'We can't be sure that's Avernus,' Yamil Cho said. 'For one thing, we don't know how many people might be living here. For another, there is no sign of the aeroshell.'

'She must have sent it back to that settlement. Tank Town.'

'Then she has deliberately stranded herself,' Yamil Cho said. 'It's not a good sign. And even if that is Avernus, it is possible that other people might be lying in ambush. Hiding in insulated spiderholes, or under the canopies of those tree-things. There's something under the rim that I'd like to look at in more detail, too. We should make at least one more pass before we set down.'

'If anyone does pop up,' Sri said, 'it will only be some technician or assistant. No doubt scared out of her wits and easily intimidated. Avernus told us she wanted to talk, and we will talk. Take us down right now, Mr Cho. Can we land close to her?'

'I would not recommend landing on the floor of the caldera, ma'am. It's thick enough to take our weight, but it's water-ice. The retrojets will almost certainly melt the surface layer, and it could refreeze around the skids.'

'The landing platform, then. We'll hike down.'

Yamil Cho brought the Uakti back in over the caldera and the retrojets cut in. Sri was slammed against the webbing of her couch as the shuttle dropped towards the secondary cone. It hovered for a moment over the scarred surface of the platform, then settled in a cloud of condensing vapour, flexed once on its skids, and was down.

Yamil Cho broke the humming silence. 'May I point out that if Avernus really is waiting for us out in the caldera, you will of course be talking to her by radio? And you can do that without stepping outside this ship.'

'That would be rude, Mr Cho. And besides, we must show her that we are not afraid or we will lose the advantage.'

'If you insist, ma'am.' When instructed to do something he disapproved of, Yamil Cho could be as disdainful as an affronted cat.

'That doesn't mean we will go empty-handed,' Sri said. 'This is her realm, one of her secret gardens. We must be prepared for unpleasant surprises. So we will carry pistols, but we'll keep them out of sight. And if it comes to it, Mr Cho, don't shoot to kill. I didn't come all this way for Avernus's corpse. Try to hit her in the arm or the leg. A disabling shot. It will puncture her pressure suit, of course, but if it comes to it I can perform a field amputation.'

'Of course, ma'am.'

Sri followed Yamil Cho through the airlock hatch and plodded after him across the pale oblong of the landing field to a path that cut along a narrow terrace. Apart from the strange orange sky, this bleak place, set amongst bare rock above a black, brooding forest that ran down a steep hillside, reminded her of her little kingdom in the Antarctic. She thought of her sons. Alder presiding over the research station; Berry sleeping innocent and unaware in his hibernation coffin aboard the Glory of Gaia. If only they were here right now, to witness her triumph! Well, she would tell them the story soon enough.

Lights came on inside the transparent dome as they approached it. Yamil Cho insisted on cycling through. As he prowled around inside, checking shower and sleeping cubicles, opening storage lockers, Sri walked around the flank of the dome and found a garage shelter where trikes with fat mesh wheels sat plugged into charger loops. She backed one of them out of the garage, drove it around the dome to the airlock, was sitting on it when Yamil Cho emerged.

'I think it would be best if I drive, ma'am,' Yamil Cho said.

'Be my guest.'

Sri slid over. Yamil Cho climbed on beside her and steered the trike towards a steep track that plunged into the forest of vacuum organisms. They were more like giant mushrooms than trees, black stalks four or five metres high topped by delicate black domes each knitted from four triangular leaves hooked together along their overlapping edges. All the domes trembling in a steady wind. Sri held tight to the trike's roll bar as Yamil Cho drove straight down the steep slope under the flexing canopy of this unearthly forest. Then the slope flattened out and they sped out across the ice floor of the caldera. Swerving around outcrops like warped chess pieces, and vents that lofted feathers of vapour that dropped as white snow on black ice-rock, bouncing over frozen ripples, drawing up several dozen metres from the gnarled extrusion ridge that loomed long and low over a sleeve of liquid like a lead or polnyap in Antarctic sea-ice, steaming within a layered casing of mineral deposits and surrounded by a field of bright snow.

A figure in a black pressure suit leaned on a tall staff on the crest of the ridge, watching as Sri and Yamil Cho clambered off the trike and Sri walked across the corrugated ground towards the ridge. She was filled with the cold clear knowledge that everything in her life had led up to this moment, and that she would triumph. It was inevitable. Yamil Cho drifted away to her right, making a flanking move. Let him. She walked on, skirting a low gnarled chimney puffing white vapour that fell as gritty powder, concentrating on making sure that she didn't misstep. The narrow smoking pool at the foot of the ridge was brimful with what looked very like water and probably was. Water was molten ice here. Lava. No doubt saturated with ammonia, which would allow it to stay liquid at temperatures as low as -97 Centigrade, but the ambient temperature was considerably lower than that, so there must be a source of thermal energy to keep that little pool liquid. Either the volcano was more active than it seemed, or there was a fission pile somewhere, heating the water under the ice via superconducting wires.

Things grew along the margins of the pool, sparse finger-sized spongy nubs in bright primary colours. The ice-rock ridge behind it, layered and fretted in steep little terraces, was splotched and splattered with pearl-grey lichenous discs.

Sri's suit radio beeped and she felt a sharp thrill of elation when she saw the ID tag of the person who had opened a channel. Avernus. She had guessed right, and had followed her hunch halfway across Saturn's system to this strange garden, this moment of triumph.

She answered at once, saying, 'My name is Sri Hong-Owen. I have come here to ask you to return home.'

'I know who you are,' Avernus said. 'If you want to talk with me, you can stop right where you are. And tell your friend to stay where he is, too.'

'That's far enough, Mr Cho,' Sri said.

'Of course, ma'am.'

He stood a hundred metres away at the far end of the ridge, a little below the level where Avernus stood.

'I have come a long way to meet you,' Sri said to Avernus. 'I stole a ship and abandoned everything I own on Earth. And I have left one of my sons hostage on one of the Brazilian warships. I hope you understand that I came here with the best of intentions.'

'For my part, I'm giving you a chance to explain what you want from me,' Avernus said.

'The vacuum organisms on the slopes - I would guess that they don't use sunlight as an energy source.'

'They would grow very slowly if they did.'

'There's very little in the atmosphere that can be used as a non-fermentable energy source,' Sri said. 'And I noticed that they grow only on the inner slopes. Perhaps they utilise the thermal energy of the caldera.'

'They generate electrical energy from temperature differentials in their tap roots,' Avernus said.

'In that case,' Sri said, 'why do they so closely resemble trees?

Forgive me, but it suggests a certain poverty of imagination.'

She ached to understand everything that Avernus had created here, but she also wanted to prove that she was the venerable gene wizard's equal, worthy of her respect.

'The parasol trees need a large surface area to absorb hydrocarbons from the atmosphere,' Avernus said, and explained that the leaves were sheets of grapheme overlaid with fine veins of catalytic polymer that grabbed organic molecules from the air and pumped them through a matrix of liquid methane to the trunk, where they were spun into more complex molecules.

'I might have cut something like a sponge,' Sri said. 'Something that could funnel air currents through large internal surfaces. It would be much more efficient.'

'There are sponges growing in the volcanic pool at your feet. At least, their genetic structure owes more to sponges than to anything else. There's a little holothurian in the mix, a little archaebacterium, but it's mostly sponge.'

'Oxidising ammonium to provide free electrons.'

'Of course.'

'Trees on the slopes; sponges in the pools. Also lichen analogues on the rocks. It's very like Earth,' Sri said, putting a snap of disapproval in her voice.

'We carry a standard of beauty from Earth,' Avernus said. 'It pleases me to use it to inform my gardens.'

'People like us need no common standard,' Sri said. 'And anyway, it's purely random. We should be free to create anything we want.'

'I freely chose to create this.'

'We could do much together. With no limits but our imaginations.'

'I would be able to do what I wanted?'

'Of course.'

'Even though you want me to surrender my freedom to you.'

'I risked everything to come here and talk to you because I know that I can help you. I can take you to a place of safety. I can give you anything you need. A place to work. People to help you. Every resource. I can be your advocate, your sponsor - even your collaborator, if you wish. Anything you want. But without me, you're just another refugee.'

Avernus seemed to consider this for a moment, then asked Sri to kindly tell her friend to move no closer.

'I'm trying to get a better view of the pool,' Yamil Cho said, with a silkiness that Sri hadn't heard before. 'I didn't mean to scare you.'

'And I don't want you to come to harm,' Avernus said.

She was leaning on her staff, gripping it at shoulder height with both hands. Its slim black shaft was shod at either end with what looked like silver and overtopped her helmet by half a metre or so.

'Is that by any chance meant to be a threat?' Yamil Cho said.

Sri told her secretary to keep his mouth shut and stay right where he was, then said to Avernus, 'I'm your last best hope. If you fell into the hands of other people, they would strip you of everything you know. It wouldn't be pleasant, and in the end they would discard you.'

'They would have to catch me first.'