'Only if his interests coincide with yours. If they do not . . . well, he sold out Speller Twain to save himself, didn't he? And we can't be sure that he told you the entire truth.'

Mother and son sat close together amongst a scatter of cushions and pillows in the glass blister. Night had fallen in the biome. Alder's elfin face was underlit by the glow of the slate in his lap, which was playing a recording of the interview with Loc Ifrahim. Watching him study changes in the dilation of the diplomat's pupils, Sri felt a tender, helpless maternal love thicken her blood. She had cut her son's fatal attraction herself, from the architecture of his cheekbones and the classical proportion of his limbs to his feverish warmth and honey-sweet pheromone-laden scent, but she wasn't immune to his charms. Her beautiful golden boy. She was so very glad that she had brought him. He would turn sixteen soon enough: it was time he learned how really important business was done, and there was no finer opportunity than this, the ground floor of a deal of historical magnitude. And he would be of great help to her, too; his charm and charisma were going to be invaluable during public appearances.

Alder said, 'He certainly appears to be telling the truth. But he's a diplomat and they're trained to pass simple lie-detection tests.'

'There's no need to work out how much of his story is true and how much is mere self-aggrandisement. Instead, we should think about which part of it would do us the most harm if we acted on it and then found it to be untrue.'

A crease appeared above the bridge of Alder's nose as he thought about this. 'That's why you turned down his offer to spy on Speller Twain. It would put you in his debt. He would have power over you.'

'Also, it would help him more than it would help me.'

'Because he isn't innocent in this,' Alder said. 'He was working with Mr Twain. And after the failure of their plan to frame Macy Minnot for Ursula Freye's murder, he wants to silence Mr Twain before Mr Twain betrays him.'

'And who would Mr Twain betray him to?'

'The peace officers?'

'He has diplomatic immunity. The most they can do is request his expulsion from their city.'

'Well then, to Euclides Peixoto, I suppose. Or to the ambassador. Mr Ifrahim would be in a lot of trouble if they found out.'

'The ambassador is of no account because Loc Ifrahim is working for someone with considerably more authority,' Sri said.

'Do you mean the general?' Alder said.

'Or one of the general's many friends and allies. As for Euclides, he was given charge of this project by his great-uncle because something as important as this has to be helmed by one of the family. It was an offer he couldn't refuse, but he has always made it clear that he has no real allegiance or commitment to it. Even so, his inaction over Ursula Freye's murder is due to something deeper than mere indifference. He's definitely gone over to the other side. I always suspected it. Now I know.'

When Sri had met with Euclides Peixoto yesterday, straight off the ship, he'd shrugged away her questions about Emmanuel Vargo's death, Ursula Freye's murder, and Macy Minnot's defection, telling her that he'd rid himself of the two Fontaine bitches, and fixed the sabotage attempt by growing up clean cultures of the diatom; as far as he was concerned everything had worked out pretty well.

Alder said, 'There's no hard evidence that Euclides has changed sides. And besides, even if he isn't the best man for the job, Oscar put his trust in him.'

'And Oscar is never mistaken.'

'Not about things like that.'

Sri and Alder had spent many hours discussing the ways in which the relationships and affiliations between the Peixoto family's key players were growing ever more polarised. Like his mother, Alder believed that peace and reconciliation was a better option than war, but he also believed that the family's green saint still had significant power and influence, a view that in Sri's opinion was supported more by sentiment than reasoned judgement.

'Perhaps Oscar was right to trust Euclides when he put him in charge of this project,' she said. 'But things have changed since then. Since Maximilian's death.'

'But you haven't changed your mind.'

'You know that I haven't.'

As always, Sri was tempted to add not yet, but she didn't want to start an argument about her divided loyalty, her work with Oscar Finnegan Ramos and her work on Project Oxbow, not when she wanted to concentrate on the matter at hand. And besides, she really did want the biome project and everything associated with it to succeed. Not only because it would be no light thing to betray Oscar Finnegan Ramos, but because she had put so much into it, and it truly was magnificent. And because its success would surely be a major boost to her ambition to collaborate with Avernus.

She said, 'What I believe has nothing to do with what Euclides believes. And it's obvious that he believes that it's in his best interests to switch sides, go over to the pro-war faction. It's the only way to explain his indifference to this crisis.'

'Or maybe it's just that you don't like him,' Alder said, still nettled by her insinuation that Oscar's judgement might be less than perfect.

'What's to like? He's vain and arrogant, and he isn't especially intelligent, either. Like many of the scions, he's noblesse without the oblige. They inherited their positions, Alder, but we earned ours. That's why we are better than them, even though they own most of the world. That's why we will survive this. Whatever happens, we'll survive.'

There was a brief silence. Then Alder said, 'Whatever happens.'

'Good. Now, how should we deal with Loc Ifrahim, and his insinuation that Speller Twain may be planning to assassinate me?'

'We can't make a direct move against Speller Twain because he is still working for Euclides Peixoto. And we can't expect Euclides Peixoto to help us. So I suppose we will have to pretend to trust Loc Ifrahim.'

Sri hugged her darling clever boy, kissed him on the forehead. 'As long as he thinks we trust him, we have him in the palm of our hand.'

'Speller Twain may not be the one coming after us,' Alder said. 'It may be Mr Ifrahim. And if he is working for the general . . .'

'No,' Sri said. 'Arvam needs me. That's why he gave me that blunt warning at the funeral. If Mr Ifrahim was telling the truth, if I am the target of an assassination plot, someone other than Arvam will be behind it.'

'Still, it may not be wise to allow Mr Ifrahim to get too close to you in future.'

'The assassin, if he exists, won't make his move yet. It will be in a public place, where it will make the greatest impact.'

'The opening ceremony.'

'Exactly. Meanwhile, we behave as if nothing has changed. Call up your files. You can brief me on who I'm meeting tomorrow.'

11.

Sri had already endured a tedious welcoming ceremony - bad speeches full of uninspired platitudes, a wearisome round of introductions, dull conversations with duller dignitaries. There was worse to come. The day after she met with Loc Ifrahim, the tours and meetings began in earnest.

The sessions where the Peixoto family's negotiators outlined the advantages of trade and details of possible deals took up hours of her valuable time, but at least they were amusing in a lowbrow, circusy kind of way. Unlike government committees and family conferences in Brasilia, the presentations and discussions were attended not only by senators from the city and outlying settlements but also by any citizens who pitched up out of interest or curiosity. There seemed to be little in the way of protocol or rules of debate. Anyone could say anything to anyone else at any time. Seniority meant nothing. Arguments were won as much by a refusal to give way to others as by logic, and a great deal of time was wasted in arguing for special interests or airing old grievances that had nothing to do with the topic at hand. One day, some old coot representing a Russian community on the far side of Callisto spent two hours making a filibuster speech in an attempt to shoehorn advantageous terms for his family into a discussion document. And when he finally gave way, another interloper started reading out a list of pointless questions that took up the rest of the session, which finally broke up in disarray.

Sri wore her spex throughout, recording everything without a qualm. Nothing important would be decided at these meetings, so it wouldn't in any way damage the interests of the peace and reconciliation faction if Arvam Peixoto was privy to it. The family's hard-shelled negotiators would hammer out details of any deals later on, in private sessions. From what she'd seen so far, Sri was of the opinion that they were more than capable of talking rings around the hapless Outers, and in any case the Outers were quite open about their interest in the new fusion motor. So far, it looked like Oscar Finnegan Ramos's long-term plan to ramp up funding of applied science, vigorously contested by those members of the family who believed it to be a waste of resources, was going to be vindicated.

She recorded the endless round of tours, too. The Callistans were inordinately proud of Rainbow Bridge and seemed eager to show their distinguished visitors every nook and cranny. There was a tour of the biome, of course, and of the tunnel farms and the undergardens that processed the city's waste, typical small factories and model apartments, pocket parks and the cemetery forest . . .

Sri wasn't cut out for diplomacy, but she had to pretend to take an interest in everything she was shown and endure the impertinent questions of ordinary Outers, who seemed to believe that they had a right to know everything about anyone. It didn't help that many of her hosts were only a few years older than Alder, enthusiastic, animated, sincere, and fantastically optimistic. Sri thought they were far too idealistic and naive, and she didn't think much of the cosmetic cuts of which they were so proud, either. She had no problem with adaptations to low gravity - alterations to the mechanism of bone-calcium reabsorption, fine-tuning balance and proprioception, two-chambered microhearts in the femoral and subclavian arteries to stop blood pooling, and so on. But the plethora of smart tattoos, spurs and scales and a host of other silly fancies were good for nothing but advertising the shallow vanity of her hosts, who blithely assumed that they were the pinnacle of human evolution, and their city a Utopia, and were increasingly puzzled and embarrassed by Sri's cool indifference to their clumsy propaganda.

The only tour that really interested her was the last in an interminable series that had taken up far too much of her time: a trip to one of the vacuum-organism farms out on the cratered plain north of Rainbow Bridge. Sri, Alder and their hosts travelled in a rolligon with a mostly transparent cabin, like a goldfish bowl on six fat mesh wheels. It moved at a stately pace along a broad road that sliced through low ridges thrown up by the seismic energy of ancient impacts. It was night. Jupiter's fat disc dominated the black sky. Stars were flung with careless extravagance everywhere else, thousands of them, hard untwinkling points of every colour.

The farm was set in a shallow crater ten kilometres across and half-buried in the plain. A gap in the slumped ridge of its rimwall opened out to reveal a patchwork of fields of vacuum organisms stretching away to the curved horizon. Other farms to the east and west were vast monocultures of vacuum organisms that synthesised plastics, slowly accumulated CHON food that, if the conventional crops grown in tunnels under the city failed, could feed the population for several months. And there were thousands of hectares of vacuum organisms that accumulated on their surfaces coatings of pure graphite used in the manufacture of construction diamond or fullerenes. The fields of this farm, though, were nurseries for varieties that after propagation would be transplanted at metal-rich sites scattered across Callisto. Some were chemoautrophic, obtaining their energy from oxidation of elemental sulphur and ferrous iron; others used sunlight and electrochemical energy generated by temperature gradients in the crust, which their holdfasts penetrated for dozens of metres; all grew dense, finely-branched webs deep into the ice, leaching out metals and sequestering them in harvestable nodules. Metals, mostly derived from meteoritic impacts, were in short supply on Callisto and the other moons of Jupiter. The bolides and fracture-bed remnants of large meteorites could be mined, but a myriad smaller impacts had salted the ice with thin deposits that only vacuum organisms could extract efficiently.

Vacuum organisms inhabited the borderland between machines and life: hives or self-organising swarms of various kinds of microscopic machines that behaved like cells in living organisms, making copies of themselves, changing their shape and metabolic repertoire according to simple rules programmed into giant self-replicating molecules analogous to DNA. They grew and multiplied in temperatures as low as -220 Centigrade, forming structures that harmoniously complemented the stark moonscapes. The most common morphological types echoed the structure of lichens, from rugose or ridged scabs to filamentous tangles. A few elaborated delicate fans and fretworks, or flat fins rising in long rows from the adamantine ice, always orientated north to south to maximise the amount of light they could gather. And because insolation was low around Jupiter - just four per cent of the average amount of light striking Earth's surface - every type of vacuum organism was a deep, light-absorbing black. Travelling in the rolligon along the raised road that cut through the fields of tan dust was like passing over a vast page of some ancient manuscript printed in the hieroglyphic script of a forgotten language.

Alder was fascinated by the robots that stalked along the rows of vacuum organisms, and by the fact that most of the farm workers were convicts serving rehabilitation terms. As he and Sri were shown around the laboratories where Avernus had worked in the early days of the Outer System, when creating vacuum organisms and improving the yields and varieties of the limited number of conventional food plants had made the difference between survival and failure, he asked all kinds of questions, shamelessly deploying his knack of acting much younger than he was, eager and charming and innocent as a puppy.

The laboratories were housed in low-roofed chambers with internal walls built of blocks of tan brick manufactured from compressed dust, their mortar courses blackened by age. Many of the rooms in the living quarters were empty - the convict labour force was housed in a new facility to the south - and most of the laboratories were as dark and empty as the living quarters, while the equipment in the rest was antiquated and clearly not much used. And despite the crisp linen, sparkling crystal and china, and fresh flowers on the tables, the commons where Sri and Alder and their hosts ate lunch seemed forlorn and derelict. It seemed that little research was done here these days.

Sri, who had first made her reputation by developing an artificial photosynthetic system that was almost five per cent more efficient than any designed by Avernus, told her hosts about the vacuum organisms grown around the lunar city of Adiena. 'You could cultivate them here, if you rigged lights. Or use vacuum organisms that utilise electrochemical energy, as in the first strains. I have cut many variations on those. You can plug fields of them straight into an electricity supply and stand back and watch them grow. I'd have to splice adaptions to the much lower surface temperature, of course, but it isn't a problem. I bet I could increase productivity by an order of two magnitudes.'

One of the scientists who worked at the laboratory said that it was all very interesting, but they really had no need to increase efficiency. The population of Rainbow Bridge was stable, and conventional farms were currently overproducing foodstuffs.

Sri got blank, evasive looks when she asked what would happen if the population began to increase suddenly. If, say, there was a sudden rise in the rate of immigration.

'I don't think you can dismiss it so easily,' she said. 'You have a lot of empty territory here. Millions of square kilometres. Many of the people on Earth who are squeezed into cities would jump at the chance to homestead.'

Her hosts politely expressed doubt that people from Earth would really want to come here, and pointed out that in any case it wasn't economically feasible. Sri retorted that most people had been confined to cities as the regreening of Earth progressed, and despite extensive anti-birth programmes the global population was still increasing because people were living longer. Sooner or later emigration was inevitable, and not just to the Moon, which could not support many people anyway, because of the lack of water. The new fusion motor meant that travel to the Outer System would be much easier, and in any case it wasn't very expensive, right now, to pack people into hibernation coffins and send them off in ordinary freighters.

She was trying to get a reaction from the Outers, but it was like prodding sea anemones. After the first couple of jabs they closed right up. Only Devon Pike, an ancient gene wizard who had some kind of honorary position at the laboratory, stood up to her.

He was a rail-thin but vigorous old man with a shock of white hair, a first-generation Outer who had worked in this facility with Avernus more than eighty years ago. From her homework, Sri knew that he had a small talent for patching traits from one species to another but showed little imagination. An able technician rather than a true artist.

'The fact is, madam, Rainbow Bridge is the oldest and largest settlement in the Outer System,' he said. 'It was founded almost a century ago, and despite longevity treatments and the early period of forced population growth we are still a little under twenty thousand souls. We live within our means. We do not intend to repeat the mistakes of Earth, and considering that repairing the damage caused by overpopulation and the Overturn is now akin to a religion, I am surprised that you believe that we can survive what you, on Earth, very nearly did not.'

'Like it or not, the new fusion motor will change everything,' Sri said. 'It will effectively shrink the distance between the systems of Jupiter and Saturn, and allow you to explore and exploit new territory. And it will also bring Earth and the Outer System together.'

'Then perhaps we'd be better off without it,' Devon Pike said.

'It exists, grandfather,' one of the young Outers said. 'We can't unmake it.'

'It will put Neptune and Uranus in easy reach,' another said. 'The Kuiper Belt too.'

'We have no need for expansion,' the old man said, and turned back to Sri. 'You took the Moon from us. Also Mars, although you've done nothing with it since you slaughtered the Martians. Now you want to come out here and cause more mischief.'

'Mars was attacked by the Democratic Republic of China - a country that no longer exists,' Sri said. 'It's ancient history. Times have changed. We acknowledge that on Earth every day, as we strive to undo the ecological crimes committed by our great-great-grandparents. And if I may be candid, I am amazed to find that there are people here who want to maintain the status quo simply because it suits them. You are against expansion. I suppose you are against the biome, too.'

'The biome is a mistake,' the old man said. 'I have the greatest respect for Avernus. I do not doubt her generosity. But we don't need to be reminded of what we left behind. We have made new lives here.'

'New? When was the last time these laboratories produced a new strain of vacuum organism? Not some modification or minor improvement to an existing strain, but something entirely novel.'

'Well, I suppose you would have to ask the director . . .'

'I don't need to,' Sri said. 'Your research programme is at best trivial. Hobbyist stuff. You had the advantage over us for a long time, sitting out here with your archives and genome libraries, but we are catching up now. We have the energy and spirit and vision that you have lost.'

Devon Pike spluttered out some reply, but Sri paid no attention to it. She felt a bright singing in her head. This wasn't propaganda. She had no time for propaganda. She really and truly believed it. At the neighbouring table, Alder was chattering away with a posse of younger scientists, handsome and slim in his red suit-liner. What a team they made, she thought fondly. Her hosts, of course, pretended to be politely amused by her forthright bluntness, and tried to steer the course of the conversation away from the reefs of controversy, but she cut through their babble. 'You achieved much, once upon a time. I admit it. You did more than survive. You created new ways of living. You kept scientific research alive. But you have lost the frontier spirit that drove you to do all those wonderful things. Societies as well as people become afraid of change as they grow older. It's human nature. The young have adventures while the old sit at home and nurture their memories. But the plain fact is that it is time to let go of the past. It is time to look ahead. This is supposed to be a democracy. Everyone has an equal say; anyone can put an issue to the vote. But for too long, Mr Pike, your generation has had a disproportionate voice. If you don't believe me, ask your great-grandchildren.'

'They should not forget what was done to us by Earth,' Devon Pike said stubbornly. 'What happened on the Moon, and Mars. Why we came here.'

Sri looked around, but apart from the old gene wizard none of the people - not even the young Outers - would meet her gaze.

'Perhaps Avernus has a better outlook on the future,' she said. 'I look forward to finding out.'

Sri knew that she and Avernus had much to talk about. Her confidence was unassailable. She wasn't the most influential gene wizard on Earth, not yet, nor the most experienced, but she was certainly the best. It was only natural that Avernus would want to meet someone who might be her equal.

After the biome project had been finalised, Sri had done everything she could to reach out to Avernus. She had even sent to the gene wizard's only permanent home, in Paris, Dione, a signed hard copy, bound in her own vat-grown skin, of the research paper that had made her reputation. But so far there had been no response, no hint of contact. She'd been on Callisto for eight days now, and she still didn't know if Avernus would be present at the opening ceremony. Her hosts retreated into maddening vagueness whenever she asked them about it, which almost certainly meant that they didn't know either, but were too polite to admit it. Alder had made little progress either, and none of Sri's contacts in the Peixoto family and the Brazilian government back on Earth had any hard information about Avernus's plans or whereabouts. Even her sponsor, Oscar Finnegan Ramos, had drawn a blank.

'She has always been a shy and elusive creature,' he'd told Sri, in his last message. 'Perhaps you know that I met her only once. A hundred years ago, it would be. Yes, just before the Overturn. It was a conference about metabolic pathway design in the first vacuum organisms. She led the research in that field, of course. She was years ahead of the rest of us. She'd been invited to give the speech at the plenary session, and right up to the last moment no one knew if she would turn up. I was going to take her place. And then, suddenly, a few hours before the speech was due, there she was, standing at the back of one of the open discussions. You can imagine the fuss. She was mobbed. As for her speech, well, I think it gave at least three people ideas that made their careers, and then she was gone. So don't worry, my dear. She will be there or she won't be there. You won't know until the day.'

Sri couldn't tell Oscar that there was a strong possibility that someone - Speller Twain, Loc Ifrahim, someone -might be planning to assassinate Avernus. That they might be planning to assassinate her. Not just because she didn't trust the encryption on the radio link and the Outers were almost certainly listening in, but because Euclides Peixoto was probably eavesdropping, too. Not to mention General Arvam Peixoto. She was surrounded by enemies. She could trust only Alder and her secretary, Yamil Cho.

Immediately after the visit to the vacuum-organism farm she met with the construction crew for updates on their work, and then briefly talked with the young diplomat, Loc Ifrahim, who told her that he had learned something of great interest.

'Mr Twain has been visiting the free zone in the city.'

Sri pretended that she didn't know anything about the free zone and let Loc Ifrahim describe it and its customs to her.

'There's a saying that what happens in the free zone stays in the free zone. But I have heard a rumour,' Loc Ifrahim said, 'that he has been meeting with citizens who oppose the project and the whole idea of reconciliation. There are people, I am sure you know this, who would do anything to make sure that this project will fail.'

'Do you know who these citizens might be?'

'Alas, I don't. Not yet. But I do know that Ursula Freye visited the free zone several times before she was murdered. There is a connection, ma'am. I am sure of it. I will continue my inquiries, and you can rest assured that if I discover anything I will tell you without delay.'

'He wants me to think that Speller Twain is plotting against me,' Sri told Alder a little later.

'How do you know he isn't telling the truth? After all, Speller Twain definitely killed Ursula Freye.'

They were lying side by side in the blister. Alder was spooning up the curdy flesh of a custard apple.

'Do you remember the peace officers I talked to?'

'Of course.'

'The city government told them to abandon their investigation into Ursula Freye's death because it was politically sensitive. They weren't happy about that, and were very interested when I told them that Loc Ifrahim had offered me Speller Twain's head on a plate. They think as we do. That Speller Twain and Loc Ifrahim were both involved in Miz Freye's death, and that Loc Ifrahim is using Speller Twain to divert attention so that he will be free to make his own move.'

'But how can they help us if they have been ordered to abandon the investigation?'

'Like every kind of police, they are prone to bending the law when it suits them. They have been keeping a discreet watch on both Speller Twain and Loc Ifrahim. That's why I knew that Speller Twain has been visiting the free zone before Mr Ifrahim told me about it. I even know what he's doing there. It has nothing to do with any kind of plotting. He is visiting a club where people have old-fashioned straight sex while wearing masks and robes.'

'Perhaps the sex is a cover.'

'There is no doubt that Speller Twain killed Ursula Freye. Perhaps he was ordered to do it by Euclides Peixoto. Perhaps Loc Ifrahim persuaded him to do it. Perhaps it was his own idea. But the peace officers are convinced that it had nothing to do with any faction in the city.'

Alder popped a spoonful of seeds and pulp into his mouth and said, 'I think I know why you don't want to make a preemptive strike against Mr Twain.'

Sri smiled. 'You do?'

'You want one or both of them to make an attempt on Avernus's life. You save her, and she is grateful . . .'

'And she teaches me everything she knows? It's a pretty fantasy. But I'm afraid that's all it is - a fantasy. Something from one of your sagas.'

Alder put on a sulky look, half-lowering his eyelids, pouting. It made him seem even more delectable. 'Why don't you stop teasing me and tell me what you are planning? I know you aren't simply going to wait and see what happens.'

'As a matter of fact, that's just what I'm going to do.'

'So I don't have to worry,' Alder said. 'You have made arrangements to deal with everything. You don't need my help.'