'Don't be silly. Why would I have brought you all the way out here if I didn't need your help, your special talents? Making friends, for instance. I'm good at upsetting or intimidating people, but as for being friendly . . . For that, I need you.'

'Well, you made me the way I am.'

'Tell me what you were talking about at lunch today. You seem to have made some friends amongst the younger scientists at the farm.'

'Oh, it wasn't much,' Alder said. 'Except for one thing, perhaps. Although, compared to your plans, it won't seem very exciting.'

Sri knew that he was aching to tell her what he had discovered, but had to tickle him and kiss him before he gave in, telling her that several of the young scientists working at the research farm had invited him to visit a little grotto that had been the prototype for several of Avernus's later projects.

'What kind of grotto?'

'Just a little crevasse,' Alder said. 'With vacuum organisms growing in it. It's old, though. Avernus made it when she was working on that farm, eighty years ago or more.'

'What kind of vacuum organisms?'

Alder shrugged.

'Why don't I know about this?'

'It was discovered by some of my new friends two years ago. They've kept it secret ever since.' Alder explained that fourth-generation citizens of Rainbow Bridge liked to go hiking and camping in what they called the back country. 'They stay out for up to a week, travelling on foot for several hundred kilometres. They say that you can't understand the land unless you walk it. It sounds like silly mysticism, I know, but they are very serious about it.'

'They spend all this time out there in their pressure suits?'

'They hike between shelters and oases. It's something they have been doing for more than ten years now. There are different tribes with different totems, and they follow different paths. At least, I think that's how it works. Burton spent a very long time explaining it to me, but most of it sounded like gibberish.'

'Burton is one of the people who wants to take you to this grotto.'

Alder nodded. 'It isn't far from the research farm. A hundred kilometres or so.'

'And Burton and his friends-'

'Her friends.'

'They want you to walk a hundred kilometres.'

'I've hiked further on the Moon.'

'With Yamil Cho, and with a caravan of rolligons following you. Perhaps Yamil should go with you.'

'I don't think my friends would like that,' Alder said. 'This is one of their secret, special places. They want to share it with me now because I'm their new best friend. And really, it isn't as risky as it sounds. If they get into trouble they can call up a gig.'

His look was one of mute appeal. He'd set a treasure at her feet and wanted to be praised and rewarded. After a moment's thought, Sri decided to give in. It was time that she gave him some of the responsibility he craved. It would show him that she trusted him, and then there was the grotto itself, almost certainly one of Avernus's creations, full of who knew what secrets . . .

So she hugged him, told him how well he had done, how proud she was of him, and said that if any sex was involved he was to be careful not to get too carried away.

'You're finding out who you are. You should have fun while you do it. But be careful not to do anything that might come back on you later on. And if any of those convicts are involved, make sure they are screened first. And of course,' Sri added, 'you'll bring back samples and a full video record, as well as a precise reading of its global coordinates.'

'I'm not stupid,' Alder said, but he was smiling now.

Sri kissed him, full on the mouth. Tasting the silky sweetness of custard apple, and Alder's live sweetness beneath. 'You're very far from stupid. I don't know what I would do without you.'

12.

For a hundred years, the Outer System settlements had been turned in on themselves, concentrating first on surviving in hostile and Spartan environments, then on establishing robust, durable ecosystems and economic and social mechanisms. But now they were trembling on the brink of a profound social and cultural revolution. A Prignogenic phase change driven by the eagerness of many young Outers to cut loose from the old, reactionary regimes of the city states on the moons of Jupiter and Saturn. To light out for new territory. The moons of Uranus and Neptune. Pluto, Eris, hundreds of dwarf planets in the Kuiper Belt. A few wanted to terraform Mars, dismantling one of Jupiter's small outer moons to manufacture solar-sail mirrors and thousands of tonnes of halocarbon greenhouse gases that would significantly warm the planet and cause outgassing of carbon dioxide and water vapour from the frozen regolith, adding to the small but significant increase in atmospheric pressure caused by the comet dropped by the Chinese onto the original Martian colonists.

This burgeoning frontier spirit, combined with radical notions about posthuman utopianism, was beginning to cause serious social and political unrest. The Outer System's economy was built upon a barter and social ranking system based on the value of volunteer work and exchange of scientific, cultural and technological ideas and information. But now the brightest and the best of the new generation were devoting themselves to planning new kinds of social groupings that deliberately excluded themselves from the mainstream. Young people were quitting the cities for oases, shelters and other microhabitats constructed by tireless crews of robots. And they were engaged in fierce and frequently divisive debates within the collectives and family trusts that owned most of the ships in the Outer System.

The new generation of Outers wanted to use the ships for exploration and to transport volunteers eager to found new settlements in the far reaches of the Solar System, but they were outnumbered and outvoted by their parents, grandparents and great-grandparents. Because everyone in the Outer System had access to medical treatments that had increased the average life span to a little over a hundred and fifty years, the democracies of their cities and settlements, and their collectives and trusts, were really gerontocracies, cautious and reactionary, preferring discussion to decision, argument to action. The older generations had controlling interests in the ships as well as in most of the infrastructure of the Outer System settlements, asserted that they were essential for trade and commerce within and between the Jupiter and Saturn Systems, and refused to sanction construction of new ships because of the cost. Oases and shelters were built by robot labour - the robots were mostly left over from construction of the cities and it was cheaper to keep them working than to decommission them - but there were no robot factories for spaceships. Every ship was more or less hand-built, and although their hulls and lifesystems could be spun from diamond and fullerene composites manufactured from carbonaceous deposits easily mined or extracted from the icy regoliths of most moons, fabrication of their fusion motors and control systems required expensive rare earths and metals.

The would-be explorers and colonists were attacking this problem with vigour. They had worked up plans to set up robot factories that could settle on suitable asteroids and mine and refine metals that would be flung towards Jupiter and Saturn using rail guns built on site, and had designed ships equipped with lightsails and propelled by fixed lasers, or with sophisticated chemical reaction motors built from ceramics and fullerene composites. These slowboats might take a decade or more to reach their destinations, but their passengers would sleep out the voyage in hibernation. The younger Outers were determined to overcome their lack of financial and political leverage with their energy, ingenuity, and determination. They had time on their side, of course. Despite gerontological treatments and sophisticated medical procedures and therapies, simple mortality meant that sooner or later the rising generation would gain control of their families' trusts and collectives. But by then they would be as old as their grandparents were now, and they were too eager and too impatient to wait. Almost every sociopolitical model predicated breakout within a decade. If Earth could not reinforce its ties with the city states of Jupiter and Saturn and help to strengthen their conservative regimes, the Outers would diverge so quickly and in so many unpredictable ways that it would become impossible to find common ground with them. And that would make war inevitable.

But the new generation had not broken completely with the past. They admired and revered with an almost holy passion the work Avernus and other gene wizards had done in the early years of the Outer System, the novel designs for vacuum organisms and closed ecosystems that had made it possible to build permanent settlements on the moons of Jupiter and Saturn. Avernus was their green saint, their Darwin, their Einstein, an enigmatic genius shrouded in legend and rumour, a major inspiration for their own radicalism, the ambitions and yearnings they had not yet fully formulated. Sri found it very interesting that Alder's new friends had kept their discovery of the grotto from their elders, and very encouraging that they trusted Alder with their secret. If she ever got the chance to meet Avernus, the encounter would no doubt be encumbered with diplomatic protocol and ceremonial niceties. There would be little or no chance for any kind of frank discussion, scientist to scientist. But if Alder could get as close to the members of Avernus's famous crew as he had to the young scientists of the vacuum-organism farm, he might be able to open informal channels that could be used to keep communication flowing and to keep track of Avernus after she left Callisto.

But even now, with only a few days to go before the biome opening ceremony, no one in the Brazilian embassy or in the Peixoto family's crew had been able to get anyone in the city to confirm whether or not Avernus would be coming to Rainbow Bridge. The Luis Inacio da Silva, eavesdropping on the Jupiter system's traffic control, had turned up nothing useful. There was plenty of chatter about the gene wizard on the social boards, but nothing substantive. Alder came back from his trip to the grotto with pictures and samples of elaborate fluted and rippled growths of chemoautrophic vacuum organisms that had been growing in their secluded environment for more than eighty years, but he had no news of their creator.

At last, Sri stepped on her pride and her caution and invited Loc Ifrahim to her suite again. He fed her scrappy bits of evidence against Speller Twain and repeated his offer to 'deal with the problem', but said that he had heard nothing about whether or not Avernus would be attending the opening ceremony. It seemed that no one knew, and the absence of any hard facts made Sri anxious and impatient and prone to sudden squalls of foul temper that kept Alder and Yamil Cho on tenterhooks. And then, at an official reception the day before the opening ceremony, Euclides Peixoto sidled up to Sri and said, 'She's here.'

'Who is here?'

'Avernus - who else? If I were you I'd get yourself some new informants,' Euclides Peixoto said, 'because they definitely aren't as good as mine, and I'm not even trying to get close to the crazy old witch.'

This was in the central courtyard of the Greater Brazilian embassy. It was tented with swathes of pastel silks, its walls were hung with huge explosions of flowers and ferns, and its floor was carpeted with dried rose petals that yielded a heady musk as they were trodden underfoot by the great and the good of Rainbow Bridge, Brazilian diplomats and trade delegates, and representatives from Minos, Europa and other cities and settlements of the Jupiter System. The biome construction crew was huddled in one corner, clearly ill at ease amongst the finery and ritual courtesy, and in their uniform coveralls drabber than anyone else in the crowd, including the people serving cocktails and canapes and the string quartet that was playing selections of Haydn and Mozart. The courtyard was so crowded that if someone moved, all the people around them had to move too, so everyone was slowly rotating around everyone else like gears inside an ancient and especially complex clock mechanism. Sri was standing toe-to-toe with Euclides Peixoto, enveloped in a little cloud of his cologne.

'I never doubted that Avernus would come,' she said coolly. 'The biome was her idea. She underwrote the cost of its construction. So of course she would want to be present at the start of its quickening.'

Euclides Peixoto's smile widened to show most of his startlingly white, even teeth. He was wearing some kind of ridiculous uniform that Sri reckoned was of his own invention: grey jacket and trousers with pink piping, a slab of medal ribbons on his chest, a grey cap with a polished black visor pulled low over small and close-set eyes that always reminded Sri of some kind of mustelid. A weasel or stoat; a sneaky little raptor sidling through undergrowth, searching out tender prey.

'There's no "of course" about it,' he said. 'Oh, I know how you scientists have to assume something is true before you can work out whether or not it is. I know you're natural-born optimists. But this isn't science. It's politics. And as my daddy always told me, never assume anything in politics, 'cause it'll make an ass out of you and me both. Avernus is paying for the biome, sure, but she hasn't shown a jot of interest in the design, hasn't said a single word to anyone involved. To us, or to our hosts here in the city. We don't even know if she likes what's being done in her name. So if you'd asked me yesterday if she was going to turn up, I might have said, "Don't bet serious money on it." But I definitely wouldn't have said "Of course."'

'You must be disappointed to be proven wrong.'

'Don't get your hopes up about meeting her. She's on Callisto all right, but she isn't in the city, and I don't know if she's coming to the opening ceremony. I don't even know where she's staying. But I'll tell you what I'll do,' Euclides Peixoto said, his eyes glinting with malignant humour under the visor of his cap. 'If she does turn up, I'll probably have to talk about the biome with her, even though she's isn't at all interested in what we're doing. It won't cost me anything to mention your name. In case she hasn't heard of you.'

'Thank you. But it won't be necessary.'

'It's a genuine offer. When I was a kid, I used to put different kinds of ants in ajar, see which would win. I admit to being kind of intrigued about what might happen if you two geniuses ever go head to head.'

'It's not a question of winning or losing, or who has the bigger and better ideas. It's a matter of entering into a dialogue. For the good of the family.'

'Well, you be sure to let me know how you get on with whatever arrangements you need to make with her,' Euclides Peixoto said. 'If you have trouble making contact, if your people can't do their job, I'm ready to put in a good word. Because even though you're not blood, I like to think you're loyal to my uncle. But right now I got to go press some flesh and talk some small talk. And get outside of a drink or two before I make my speech.'

Sri checked the data miner that she'd posted to keep watch on the city's boards, but it had nothing to report beyond the usual megabytes of idle speculation. She called her secretary and instructed him to find out what he could. She called Alder, lost somewhere in the reception's dense throng; he said that he hadn't heard anything but would ask every one of his new friends. Finally, she called the city peace officer, Dee Fujita. She claimed not to have heard about Avernus's arrival on Callisto, and told Sri that arresting Speller Twain and Loc Ifrahim, holding them until after the opening ceremony, wasn't an option. Not only because of Loc Ifrahim's diplomatic immunity, but also because there was no hard evidence of a conspiracy.

'We can't pull him in on suspicion,' Dee Fujita said. 'We can't even do that to one of our own citizens, much less one of yours.'

'Suspicion? He's already murdered at least one person.'

'Unless you have clear evidence that either Speller Twain or Loc Ifrahim are planning to harm Avernus, I don't have the authority to touch them. Your only option is to take it to the Senate and argue that it is a matter of the city's security. You could swear out a deposition.'

'Can you guarantee a result?'

'The Senate would first have to agree to put it to the vote. And then it would have to win the vote.'

'And then the whole city would know about it.'

'I keep forgetting that you have funny ideas about how government works,' Dee Fujita said.

'I keep forgetting that you have funny ideas about using popularity contests to make decisions vital to the security of your city.' Sri was simmering with frustration, on the edge of a tantrum. She closed her eyes, visualised the cold white Antarctic sky above an ice-flecked ocean, and said, 'If I made a deposition, it would be like declaring war against Mr Peixoto. I would have to be sure that you would back me up.'

'I'll back you up by continuing to keep watch on Speller Twain and Loc Ifrahim. Let me know if you find out anything,' Dee Fujita said, and cut the connection.

Sri couldn't leave the reception until the speeches were over, had to make small talk to people she didn't know or care about while trying to think through the implications of Euclides Peixoto's news, trying to calculate how she could reach out to Avernus in the short time left before the quickening ceremony. At last the crowd's intricate mechanism brought her face to face with Loc Ifrahim.

He inclined his head in a minimal bow, and asked her if she had further considered the matter they had discussed when they had last met.

'You've failed me,' Sri said. 'Avernus is here. And I had to find it out from Euclides Peixoto.'

Loc Ifrahim's surprise seemed genuine. 'If it's true, if it isn't yet another rumour, then none of my contacts know. Did Mr Peixoto happen to tell you how he found out?'

'I didn't ask him. I'm disappointed in you, Mr Ifrahim. Gravely disappointed. Either you aren't talking to the right people, or they aren't telling you the truth. Avernus is here. Somewhere on Callisto. Perhaps in this city, perhaps somewhere else - the vacuum-organism farm, for instance, where she used to work. I want to know where she is, where she came from, and who she brought with her. Most of all, I want to know how to contact her. If you can find out anything useful I'll forgive you for failing me, and make sure that you are handsomely rewarded.'

If he knew something but was hiding it from her, Sri wanted to force his hand. Make him give it up by bribery or by threat. And if he didn't know anything, she could still make use of him, and by making use of him keep him under close watch.

The young diplomat thought for a moment, then said, 'I have a contact at the port. As soon as this little party is over, I'll talk to her.'

'You won't wait until this is over because I need to know as soon as possible. Will you help me or not? Yes or no?'

'It may take a little time.'

'Come to my apartment in three hours,' Sri said, and turned her back on him and let the slow circulation of the crowd carry her away.

The Brazilian ambassador and the mayor of Rainbow Bridge gave speeches; so did Euclides Peixoto. His speech was short and said nothing new, but he delivered it well, crisply emphasising key phrases, winning gusts of applause that he waited out with a sly smile tucked into the corner of his mouth, as if considering some private joke. At last, Sri was able to slip away without causing a major diplomatic incident. When she reached her suite, her secretary told her that Loc Ifrahim had already arrived. He was waiting for her in the dark observation blister, a shadowy figure looking out at the lake stretched below, all black and silver in the crepuscular glimmer of the chandeliers, turning to her as she entered, telling her that he had some news.

'I leaned on my contact at the port,' he said. 'She talked to the pilots of every ship that landed there in the past week. It seems that Avernus arrived six hours ago, on a tug hauling a cargo of pharmaceuticals and luxury food items from Europa. The tug is owned by the family of its pilot, Vlad Izumi. He's twenty-eight, unpartnered, no children, a citizen of Minos, Europa-'

'She came alone? Without her crew?'

'There was one other passenger. A young girl, most likely Avernus's daughter.'

'Yuli. Her name is Yuli. Where are they now? In the city?'

'They boarded a rolligon, headed north. If you give me a little more time I may be able to find out where it went.'

'I need to know as soon as possible. And why did Mr Peixoto know about this before I did? How could she arrive here without anyone in the city knowing?'

'The embassy has been monitoring arrivals and departures at Rainbow Bridge's port, of course. Anyone can do it. The information is openly available on the net. But Vlad Izumi, the tug's pilot, is not a known associate of Avernus's, and she and her daughter weren't registered as passengers. Most likely they hitched a lift. It happens all the time. There's no border control here, no customs. I must assume that no one recognised them when they disembarked, and they didn't make any use of the phone system or the rest of the net. They simply walked away. As for Mr Izumi, he is already on his way back to Europa, but he was quite happy to chat about his passengers. It seems that my contact was not the only person to ask him about them. Speller Twain got there first.'

'I thought you were a good friend of Mr Twain.'

'I never claimed that he was a friend,' Loc Ifrahim said. 'Is there anything else that you need to know? As you can see, I'm more than willing to help.'

His smile, just visible in the faint light of the chandeliers, was a thing of beauty, winning and duplicitous.

'There is one more thing,' Sri said.

It was the prearranged signal to her secretary, who had been listening in on the conversation. When Yamil Cho stepped into the blister, lithe and neat in his black jumper and leggings, Loc Ifrahim's smile didn't change, but he couldn't quite disguise the unease in his voice. 'I came here to help you, ma'am. And I can still be of help. For instance, in the matter we spoke about before.'

'You mean killing Speller Twain?'

'Kill?' Loc Ifrahim mimed shock. 'I think you misunderstood me when I said that I could help you undo the damage he has caused to your project.'

'And did I misunderstand you when you told me that he had murdered Ursula Freye?'

Yamil Cho stepped towards Loc Ifrahim and the diplomat shuffled backward until he was pressed against the transparent wall of the blister, saying, 'Of course he did. He admitted as much to Mr Peixoto.'

'Yes, you forgot to tell me that. And because I wonder what else you forgot to tell me, I will have to keep you here for a little while. Until after the quickening ceremony, at any rate.'

Loc Ifrahim's gaze couldn't settle, moving between Sri and Yamil Cho. 'My diplomatic status-'

'We'll say that you agreed to help me with my inquiries. Or I'll show the recordings of our conversations to the ambassador, let him work things out for himself. Perhaps I can't prove that you offered to kill Mr Twain, but the implication is there.'

'Very well,' Loc Ifrahim said. 'I'll stay here and play along with your silly scheme. But I can tell you now that this won't do you any good.'

'Is that a threat, Mr Ifrahim?'

'I'm afraid it's a fact, madam,' the young man said. He had regained control of himself; his face was a bland mask devoid of any emotion. For the first time Sri realised the depth of his ambition and determination. It was something to be admired and feared.

13.

Loc Ifrahim stuck to his story: he suspected that Speller Twain was planning something, but had no idea what those plans might be. Sri was tempted to put him to the question, but it would cause all kinds of trouble if she did it without the authority of Euclides Peixoto or the ambassador, and she didn't trust either of them. After some thought, she dispatched her secretary to the embassy, where Euclides Peixoto and his security chief were quartered. If Speller Twain left the embassy for any reason, Yamil would follow him wherever he went, and make sure that he knew he was being followed. Meanwhile, Alder had discovered that Avernus had visited the vacuum-organism farm where she'd once worked, and had taken a rolligon and driven north, accompanied by her daughter and several of the young scientists who had taken Alder to the hidden grotto. Alder offered to give chase, but Sri told him that it would be a waste of time, and far too dangerous besides. Callisto's battered, heavily cratered terrain could hide entire armies, and unlike Earth it was not scrutinised by the panoptic gaze of spy and weather satellites. By now, Avernus and her little entourage could be at the grotto, or anywhere else within two to three hundred kilometres of the vacuum-organism farm.

Wherever they'd gone, Sri was certain that they would return to the city in time for the opening ceremony. She was determined to make direct contact with Avernus, tell the gene wizard about the possible threat to her life, offer to talk to her privately . . . But meanwhile she could do nothing but wait, and try to get some sleep.