They were standing in a little clearing. The leaves of a clump of maple saplings glowed red as fresh blood in the low afternoon sunlight. There was a chill edge to the clean air.

Macy said, 'Can I ask you a question, Mr Vargo?'

Emmanuel Vargo's smile showed crooked brown teeth and his eyes shone with fine good humour. 'Anything you like.'

'Are you here because someone high up in the Fontaine family recommended me?'

'I'm here because you're the best of all the microbial ecologists who were put forward. Unfortunately, political nonsense meant that I had to select someone else in the first instance. Fortunately, that same political nonsense gives me a chance to remedy the situation. You don't have much experience, but neither do most of the other candidates - the other families have been reluctant to volunteer senior personnel. It doesn't matter. In this case, where we are working in a new and unknown arena, ability counts for more than experience. And I believe that you are more than capable of doing the work. That's why I came out here to personally ask you to do me the honour of joining my crew.'

Macy wasn't the kind of woman most men would look at twice, but when she smiled, her face lost its habitually guarded expression and was as utterly transformed as a shuttered room suddenly flooded with sunlight. She smiled now, saying, 'Haven't I already volunteered? When do you need me?'

'How quickly can you pack?'

Macy flew out with Manny Vargo an hour later. The next day she started training with the rest of his crew. And now she was on Callisto. Now she had to prove her worth all over again.

It was going to be difficult. Not just because of Emmanuel Vargo's death, although that was bad enough, but also because Euclides Peixoto had taken over the day-to-day running of the construction crew. And although he was good at making speeches and flattering diplomats and representatives of Callisto's government, Euclides Peixoto knew nothing about ecosystem engineering and had never shown any interest in the design of the biome or in the training of the crew. That hadn't prevented him from telling Emmanuel Vargo how to do his job on more than one occasion. His ignorance about ecosystem engineering was perfectly matched by his lack of talent in people management, and like many men born into privilege and protected by that same privilege from the consequences of failure, he had no time for the advice of people he believed to be his inferiors.

Professor Doctor Sri Hong-Owen, who had helped Manny Vargo design the biome's ecosystem, would arrive at Rainbow Bridge in four weeks' time, riding a freighter fitted with the new fusion motor. In the interim, the project would have a better chance of success if the Peixoto family agreed to allow one of the local engineers to take over. Someone who knew what they were doing. Someone who could work alongside the crew and listen to their opinions. But that was not only politically unpalatable, it also involved a point of pride. And so the crew was stuck with Euclides Peixoto and his unpredictable whim of iron. Although he could draw on the advice of Sri Hong-Owen and a team of experts, it was entirely possible that he might take it into his head that he knew better than they did because he was on the spot and they were almost a billion kilometres away. Or if he was confronted with some problem that needed solving right away, no time to consult with anyone back on Earth, he might either freeze up or make a bad decision and out of pride refuse to back down. And of course, most of the crew couldn't gainsay him. The Peixoto family was far more conservative than the Fontaines, and even under the Fontaines it wasn't prudent to talk back to anyone with the smallest degree of consanguinity, Although you could at least bitch about the bosses behind their backs. Even that was too much of a risk under the Peixotos. Anyone caught criticising the people who owned their hides could be accused of treason, there were spies and snitches everywhere, and the punishments for disloyalty were severe, so everyone owned by the Peixotos kept their opinions to themselves. Macy was pretty sure that not even Ernest Galpa, now the most senior member of the crew, a decent old fellow who had worked with Emmanuel Vargo for twenty years, who had openly wept at the news of Manny's death, would dare challenge Euclides Peixoto if he decided on some course of action that threatened the success of the project.

Theoretically, crew members from other families could stand up to him with a degree of impunity. But Cristine Quarrick and Patrick Alan Allard came from the Nabuco family, which was even more old-school than the Peixotos, everyone knew that Cesar Puntarenas was no more than a spy who reported directly to the Fonseca family council, and Although Ursula Freye had a thirty-second degree of consanguinity within the Fontaine family, being the daughter of a second cousin of their only green saint, she was consumed by paranoid fantasies of a conspiracy that had murdered her lover. Macy could only hope that when Euclides Peixoto screwed the pooch - and she reckoned that when was much more likely than if - it wouldn't have anything to do with her sphere of responsibility. Because if he ordered her to do something idiotic, she'd probably be stupid enough to refuse, and then he'd cut her off at the knees, blacken her name, and send her back to Earth with a reputation as a wrecker. After that, she'd be lucky if she could get a job breaking rocks.

Fortunately, she didn't have much time to worry about the different ways the man could crash the project. She had plenty of work to do, and she had to do it quickly.

To begin with, the biome's microbial ecosystem - the combined metabolic repertoire of trillions of microscopic workers that underpinned the cycles of carbon fixation, nutrient recycling, and organic decomposition had to be up and running before the lake could be planted out and stocked with fish and invertebrates. Macy needed to grow up starter cultures to seed the reed beds and stromatolite reefs that would filter the lake water and recycle nutrients, and she also had to liaise with the plankton team to produce a mixed culture of bacteria, blue-green algae and diatoms that would clarify the lake water by attaching to suspended fines and elaborating mucopolysaccharide threads to form fluffy accretions heavy enough to sink out of the water column. This process of flocculation, which would not only allow photosynthesis to take place at all depths of the lake, but would also produce an organic-rich layer of mud, would be initiated by injection of large volumes of the mixed culture into every sector of the lake during the formal opening ceremony. That was due to take place in thirty-two days, after Sri Hong-Owen had arrived and the lake had reached its final level. It was an inflexible deadline. But as soon as they started work, Macy and the plankton team ran into a serious problem: the diatom they planned to use, a tweaked strain of Skeletonema costatum, wasn't growing as fast as it should when cultured in the melt water that was filling the lake. If they couldn't get the doubling rate up to where it should be, they'd not only be short several hundred kilograms of diatom biomass, they'd also have to adjust the growth rates of all the other microorganisms.

It was the kind of problem that Macy enjoyed solving. Biome engineering was more of an art than a science, an intricate game or puzzle in which everything affected everything else, its complexity increasing exponentially with the addition of each new species. Plants competed for the nutrients and light; animals grazed on plants or preyed on other animals; microorganisms broke down dead organic material and recycled nitrogen and phosphorus and sulphur into forms that other organisms could use. If a single species was removed from or added to this web, the relationships between every other species were changed in large and small ways that could not always be predicted. Macy had the useful knack of being able to hold models of nutrient and energy flow in her head and examine them from every angle, visualising their interlocking checks and balances, predicting how changes in one parameter would propagate through the system. She wasn't as good at it as Manny Vargo, who'd been able to conduct the equivalent of two or three symphonies at once, with choirs and bells and thundering organs. But she was competent, she was used to hard work and impossible deadlines, and the city had given her two good assistants and sole use of a well-equipped facility on the west bank of the lake. She had every confidence that she would succeed.

The facility was set in and around the footing of one of the big arched struts that, elaborated from spun threads of fullerene, supported the Biome's tent. At its base, the strut flared into a gourd-shaped structure ten storeys high, hollowed out with terraced apartments and rising above a plaza beside the empty black bowl of what would be a shallow bay when the lake was filled. Macy's laboratory was on the ground floor of the hollow strut, and the bioreactors where she and her two assistants were growing pure and mixed cultures of microorganisms had been set up in the plaza. That was where she was working when the crew's security chief, Speller Twain, and the youngest and newest member of the Brazilian diplomatic team, Loc Ifrahim, came for her.

It was eleven days after the lake had started to fill. Macy and her two assistants, Argyll Hall and Loris Sher Yanagita, were in the middle of a discussion about the problematical diatom culture when the two men walked in.

'We need to talk to Miz Minnot,' Speller Twain told Macy's assistants. He was a burly man with a blond crew cut and a pinched, sour glare. The sleeves of his coveralls had been ripped off, displaying muscular arms covered with military tattoos. 'It's crew business, so take off, why don't you?'

'They have work to do,' Macy said. Although she'd been expecting something like this, she was suddenly dry-mouthed and her heart was beating quickly and lightly. 'Plus, you might want to get out of range of the cameras in here - believe it or not, there are citizens who have nothing better to do than watch me work. If you want to talk privately, we'd best do it outside.'

The two men looked at each other and the diplomat shrugged and said, 'Why not?'

Macy led them past the bioreactors to the jetty that stretched out into bay's dry bowl. She headed straight for the end, ankling along in the heel-and-toe shuffle that was the best way of walking in Callisto's light gravity, putting some distance between herself and the two men. She needed a little time to compose herself and to let go of the anger and dismay kicked up by their presumption.

When she turned, she saw that Speller Twain had stopped halfway along the jetty, leaning against the rail like a casual sightseer as Loc Ifrahim shuffled towards Macy. 'Why don't you tell me exactly what's troubling you?'

she said to the diplomat. 'Then I can tell you why I can't do anything about it and get back to my work.'

Loc Ifrahim smiled. 'They told me you spoke plainly.'

He was only a few years older than Macy, his narrow, clever face framed by black hair twisted into dozens of tight braids that brushed the shoulders of his white silk suit. Officially, he was part of the trade delegation, but everyone knew that he was a government spy.

'I won't apologise for my way of speaking, Mr Ifrahim,' Macy said. 'I wasn't raised with your advantages.'

'Actually, my childhood had precious few of what you might call advantages,' Loc Ifrahim said. 'But I was lucky enough not be raised in the bosom of some strange sect that believes universal truth can be found by playing mathematical games with pi. I'm curious - do you still believe in that, Miz Minnot?'

Macy was used to taunts about her odd upbringing. She'd had to put up with them ever since she'd signed up to become an R&R labourer. 'I've outgrown my childhood, Mr Ifrahim. How about you?'

'I acquired all kinds of old-fashioned virtues which I still try to apply to the way I conduct my life,' Loc Ifrahim said. 'Loyalty to one's family and friends, for instance. How about you, Miz Minnot? I know you have no loyalty to your family because you ran away from them. But are you loyal to your friends? Do you feel any loyalty to Ursula Freye, for instance?'

There it was, just as she'd thought.

'I'm not sure that she'd want me to call her a friend,' she said. 'We're from the same territory, but that's about all we have in common. Plus, Ursula has consanguinity, and she's a stickler for protocol. She made that pretty clear during training.'

'She likes to pull rank on you. Even so, I'm sure you'd help her if she was in trouble.'

'What kind of trouble?'

'How does Miz Freye seem to you?' Loc Ifrahim said.

'I don't know. Tired and a trifle manic, I suppose. Like all of us.'

'Manic, mmm,' Loc Ifrahim said, seeming to like the taste of the word on his tongue. 'Has she told you what she's been up to?'

'You seem to have a problem with coming to the point, Mr Ifrahim. Since it isn't exactly a secret, let me speak plainly and get it out of the way. Ursula thinks that Emmanuel Vargo's death was no accident. She thinks he was murdered. She's been running around looking for clues, and now I would guess that it has caused you some kind of trouble. How am I doing?'

Loc Ifrahim's glossy black braids were strung with beads, different sizes, different colours. They rattled and clicked as he turned from Macy and gripped the rail at the end of the jetty with both hands and looked out, or pretended to look out, across the little bay. His cinnamon skin was flawless. He wore rings on every one of his fingers, and he had the neatest fingernails Macy had ever seen (her own, even though she kept them trimmed short, were ragged and broken, and the nail of her right thumb was bruised black from where she had jammed it in the sampling lock of one of the bioreactors). His perfume hung in the cold air between them, a sharp odour like orange peel and burnt sugar.

At last he turned back to look at Macy, and said, 'Do you think that Mr Vargo was murdered?'

'If you're working your way around to asking me to help you find out what Ursula's been doing, you should know that I'm no snitch, Mr Ifrahim.'

'I don't want you to help me. I want you to help her,' Loc Ifrahim said.

'Do you have consanguinity, Mr Ifrahim?'

Loc Ifrahim's smile didn't alter, but something changed behind his eyes. 'No one in the diplomatic service has any degree of consanguinity. It ensures that we are entirely impartial.'

'I don't have any either. But Ursula Freye, she has a thirty-second degree of consanguinity in the Fontaine family. And the Fontaine family own my ass. So if you want someone to persuade her to stop looking into the circumstances of Manny Vargo's death, I'm not the person to do it. If for whatever reason you don't want to talk to her, maybe you should ask Mr Peixoto to deal with this. He's full-blood family, and he's supposed to be in charge of this crew.'

'Oh, this isn't the kind of thing I want to concern him with.'

'I don't think it concerns me, either.'

'You're wrong, Miz Minnot. There are many people in Rainbow Bridge who are not at all sympathetic to this project, or to Greater Brazil. By pursuing her inquiries, Miz Freye may play into their hands and damage us all.'

'So keep her in the biome. Have Mr Twain put her under house arrest.'

Loc Ifrahim said, 'We could try to silence her, but Mr Twain thinks it would cause more trouble than it's worth. And I have to say that I agree with him. We would have to explain to Miz Freye's immediate family why we had to do it. And we can't stop Outers coming into the biome, of course, and we can't tell them why they shouldn't talk to Miz Freye. No, it really would be best for all concerned if you had a quiet word with your compatriot. If you told her that we know what's she doing, that we understand her grief, and that we want to help her in any way we can.'

Macy said, 'Is that an order, or are you asking me a favour?'

'I could ask Mr Twain to persuade you to do it,' Loc Ifrahim said. 'But I would prefer you to volunteer out of friendship and loyalty. Friendship to your compatriot, and loyalty to the crew and their mission. Because if Ursula Freye doesn't stop her silly little crusade, she'll cause trouble for the rest of the crew, she could well damage a lot more than this little project, and she'll most certainly damage the reputation of the Fontaine family. And even though you have no consanguinity, that will also damage your reputation, Miz Minnot. People will say that you should have done something about it. They will say that you were implicated in Miz Freye's crazy and completely unfounded imaginings. And I very much doubt that the Fontaine family will be pleased to hear that you stood by and did nothing to help.'

'Dress it up any way you like, you want me to do your dirty work.'

'Talk to Miz Freye. I have persuaded Mr Twain to allow you two days'

grace. After that, he will want a report on your progress. For your sake, I suggest you have something positive to tell him,' Loc Ifrahim said, and sketched a quick bow and shuffled away down the jetty towards Speller Twain, who pushed from the rail and touched the corner of one eye with his forefinger and then aimed it at Macy like a gun. Telling her, I'll be watching you.

After she'd run away from the sect, Macy had spent a couple of years on the streets of Pittsburgh. She knew all about good-cop/bad-cop routines. It would be funny, really, if she hadn't seen how Speller Twain operated. Like at the progress meeting two days ago, when Delmy March, the man in charge of the fish and mammal crew, had corrected Euclides Peixoto on some point about the timetable of the quickening. Euclides Peixoto had taken offence and told Delmy he wouldn't tolerate that kind of mealy-mouthed wrecking talk, and Speller Twain had detached himself from the wall where he'd been leaning and crossed the room in two lithe bounds and grabbed Delmy in an armlock and stuck the black spike of a jammer behind Delmy's ear, putting him into convulsions so bad he'd pretty near bitten off his tongue.

So instead of walking past the two men, who no doubt wanted to give her the benefit of some parting advice, Macy vaulted the jetty's rail and floated down four metres and strode away across the floor of the bay. Her thoughts were snarled up and some kind of physical activity was usually a good way of freeing them, but most of all, right there and then, she wanted to get away from everything, and as she came out of the bay's wide mouth she broke into a run, long fluid strides that quickly ate up distance, passing a low sandy promontory planted with young cabbage palms and yuccas, running on under the clear white light of the chandeliers and the irregular quilting of the tent towards the long oval of water that occupied the deepest part of the lake. A little to the south was the low black wall of the coffer dam that circled the site where an archipelago of tiny islands was being constructed, a last-minute change in the landscaping specifications, and beyond that was the terraced shape of the main island. The lake floor was constructed from the same material as the coffer dam, a thin skin of light and incredibly strong fullerene composite, black and finely striated like muscle, laid over an insulating substructure several metres deep that anchored it to the adamantine ice, shaped and contoured with shallows and slopes, trenches and raised table reefs. It was like running in an enormous, half-full bathtub.

Macy was beginning to sweat now. She pulled off her cap and ran on with her hair streaming behind her like the tail of a rusty comet. Running was much easier than walking in Callisto's low gravity, but changing direction was difficult because you still had the same mass but far less traction; you had to think ahead, make wide arcs around obstacles, and slow down gradually, because attempting a sudden stop was liable to make you tumble head over heels. Bill Highbridge had bruised a couple of ribs when he'd slammed into one of the boulders planted on the ridge of the main island, and Pilgrim Greeley had broken a wrist in a bad fall, but Macy had been running out on the lake bed every morning before breakfast, letting her thoughts settle out, getting ready to tackle whatever problems the day would throw at her, and she swung south easily and smoothly, moving parallel to the edge of the water that each day rose a little higher.

The water filling the lake bed from the centre outwards was now about half a kilometre across at its widest point. In another week it would be lapping at either shore, and Macy would have to take her morning constitutional along the rim road. It was already an impressive sight: a broad channel of tawny water agitated by dozens of fast streams feeding it from the infall pipes along either shore, waves running back and forth, clashing in white riffles. There was no shortage of water on Callisto of course - the moon was entirely covered in water ice, a frozen world ocean wrapped around a core of silicate rock - but at around -1700 Centigrade the ice was hard as granite. To create the lake, it had to be mined and melted, processed to remove sulphur compounds and drive off excess carbon dioxide and add oxygen, and then pumped through kilometres of heated pipes into the biome's chamber. The outfall of one of those pipes jutted from the embankment a few hundred metres away, water steaming as it spewed out in a flurry of foam, the wild smell of it electrifying Macy's blood. The ice had been frozen for billions of years, but all it needed was a little free energy to weaken hydrogen-to-hydrogen bonding and effect a phase change from solid to liquid. Like bringing a fossil back to life.

The three huge machines that mined, processed, and melted the ice, the huge tent that housed the biome, and the biome itself, represented an enormous outlay of engineering, energy, and human work and imagination. Macy was determined to honour the Outers' grandiose plans with her own contribution, but although her skills hummed in her brain and trembled in her fingertips, although she'd spent several hundred hours planning every last detail with the plankton crew and poor Manny Vargo back in Greater Brazil, back on Earth, she'd been having sleepless nights ever since she'd arrived. The dreaminess of the low gravity and the strange taste of the air, the odd noises echoing in the high-ceilinged space in the hollow base of the strut (she had taken to sleeping in the lab), all contributed to her insomnia, but it was mostly due to nagging anxieties about everything and anything that could go wrong. She was ready and willing and able to do the work she had to do, but felt as if she was surfing a standing wave of exultation and apprehension. She was here. She had made it. Yet a single misstep might wipe her out.

And now, on top of everything else, she had to deal with this little job gifted her by Speller Twain and Loc Ifrahim, that smooth-talking smiler. The problem was, Manny Vargo's death might have broken Ursula Freye's heart and made her desperate and more than a little crazy, but the woman was also a crashing snob, stubborn and aloof. No matter how distressed and lonely she might be, she wasn't about to take advice from someone as low-born as Macy, and Macy couldn't think of anyone else in the crew who might help out. Most of them belonged to the Peixoto family, and despite all the exercises designed to unify them during training they'd quickly split into like-minded factions, little groups of three or four that crossed sexes and specialities and excluded outsiders. As for the rest, Cristine Quarrick and Patrick Alan Allard, from the Nabuco family, were married and inhabited a cosy little world of their own making with no time for anyone except themselves, and Cesar Puntarenas was an unsympathetic character who enjoyed playing up to his reputation as a rogue agent.

Macy ran alongside the edge of the lapping water until she reached one of the streams that frothed down a moulded channel a couple of metres wide. She jumped the channel with ease but landed awkwardly and tumbled headlong, a long sprawling slide that knocked the wind from her lungs. Sitting up, flexing her arms and legs, discovering nothing worse than a scraped palm and what was going to be a spectacular bruise on her behind, she saw one of the little camera drones that infested the biome hanging above the edge of the lake, a fat blimp about a metre long, its underslung camera pointing in her direction. She laughed and gave it the finger, wondering just how many citizens had watched her little pratfall, and then was struck with a notion of how best to reach out to Ursula Freye.

When she got back to the lab, she told her two assistants that she believed that they might be able to help her deal with a little personal business. She put a finger to her lips when they began to question her, led them out of the lab and along the jetty, and said that what she was about to tell them was confidential, they had to swear they wouldn't tell anyone else about it.

The assistants exchanged glances. They were both in their forties but looked about Macy's age, slim and fine-boned, looming over her like a pair of friendly giraffes. Argyll Hall with his paper-white complexion and cockatoo's crest of bright red hair; Loris Sher Yanagita with her bright green eyes, pupils slitted like a cat's. Macy liked both of them. She didn't doubt that they were reporting on her every move, but they were hard-working, competent, and, in their different ways, enthusiastic. Loris was quiet, someone who liked to listen rather than talk, and talked only when she felt that she had something worth saying, but she had an intense, slow-burning ardour for her work; she reminded Macy of the way wildsiders carried fire from camp to camp, smouldering punk caught inside a fold of clay. Argyll was a more vivid character, quick-minded and impulsive, brimming with half-formed ideas, talkative and endlessly curious about how things were done on Earth, and Macy's reactions to the way things were done here. Although Macy tried to appear unshockable, she was shocked, more than a little, by the tweaks Outers made to their bodies. Argyll had spotted this at once, and made a point of letting Macy know all about his little differences from the human norm. Physiological adaptations to microgravity, cellular mechanisms that enhanced repair to radiation damage, speedier reflexes and a ballet dancer's sense of balance, changes in his corpus callosum that enabled him to survive on catnaps for months at a time or enter a sleep as profound as hibernation, and a dozen lesser tweaks, from the reflective membrane at the back of his eyes that increased his night vision to perfect pitch. When Macy had given it back to him, asking why Outers didn't go all the way and grow hands at the ends of their legs instead of feet, Argyll had shrugged and smiled and said that maybe one day they would, and Loris had said, 'Have you ever tried walking on your hands all the time? Even in our gravity, it's hard. They just aren't built for it.'

'How about tails?' Macy had said, trying to be provocative.

Loris had thought about this for a moment, calm and serious and imperturbable. 'I think they tried that in Camelot, Mimas. Of course, the gravity is lower there . . .'

Which had made Macy laugh. She liked Loris. Loris was a lot like her.

Now, before Macy started to explain why she was about to ask them for a very big favour, Argyll jumped right in and said, 'I bet this is about Mr Vargo's murder.'

Macy felt a twinge of unease. 'Were you eavesdropping, just now?

Can people listen to us out here?'

Loris shook her head.

'We guessed,' Argyll said. 'I mean, it's pretty obvious. What else would that diplomat and the security chief want to talk to you about? So, do they think they know who did it?'

'They don't think it was murder, and neither do I.' Macy paused, struck by an uncomfortable thought, then added, 'Do people in the city think he was murdered?'

'I think the latest poll has it that around sixty per cent believe Mr Vargo was killed,' Argyll said.

'There are polls on this?'

'Anyone can run a poll on anything,' Argyll said. 'How else can you find out what people are thinking?'

Loris said, ' I don't think he was murdered, but Argyll does. You should ask him what they're saying on the thread about Mr Vargo. The conspiracy nuts are having a great time.'

Macy said, 'I shouldn't tell you what I'm about to tell you, but I need your help. So promise you won't mention this to anyone, on this conspiracy-theory thread or anywhere else. Okay?'

Argyll drew an infinity sign on his chest with his forefinger and said, 'Hope to the before I do.'

'It means he won't,' Loris said. 'And neither will I.'

'We want to help,' Argyll said.

'Let's see if you can,' Macy said. 'It seems that one of my colleagues has been going out and about in the city. I need to know where she goes, if she's meeting anyone. Don't tell me you can't do it. I know that there are cameras all over the city. And they all feed into the city's net.'

She'd decided that the first thing she needed to do was find out if Loc Ifrahim had been telling the truth, find out if Ursula really had gotten herself involved in some kind of clandestine chicanery. If the woman's visits to the city were innocent, if there was nothing to Loc Ifrahim's story but devilment, then Macy could tell him to leave her the hell alone and let her get on with her work. But if she had hard evidence that Ursula was involved with malcontents or hardliners, she could use it as leverage when she confronted the poor woman and tried her damnedest to convince her that they didn't have her best interests at heart.

Argyll looked disappointed, saying, 'Is that all?'

Loris said, 'Who is she?'

'Ursula Freye,' Macy said. 'And before you start asking me questions I can't possibly answer, this isn't anything to do with Mr Vargo's death. It's all about helping a colleague of mine who's gone a little crazy with grief.'

5.

Two days later Macy rode a tram to the free zone at the northern edge of Rainbow Bridge. She'd visited the city twice before, but each time it had been to attend official functions - a kind of reception where she and the rest of the crew had been exhibited like exotic animals, and a theatre piece involving musicians, dancers, tableaux and projections in what had been billed as an interpretation of universal creation myths. Macy had recognised a couple of fragments from Genesis, but the symbolism of most of the performance had been impenetrable, the music had sounded like a train-wreck, and she'd had a hard time staying awake. So despite her forebodings about the enterprise, she felt an exhilarating mix of anticipation and liberation as she rode through the city on her own.

Rainbow Bridge occupied a froth of pressurised tents and geodesic domes of different sizes. Inside them, low-rise apartment blocks much like those Macy had helped to demolish in the ruins of Chicago were strung along streets radiating out from a central park, scattered at random across parkland, or, in the oldest parts of the city, crammed side by side, their roof gardens connected to each other by slender bridges. There were a few blocks of workshops for small-scale industries and crafts, but most of the city's factories were located in smaller domes outside the city's cluster, amongst vacuum-organism farms and refineries. The tram carried Macy through woods and meadows, down the centres of wide tree-lined streets. She got off at the last stop and put on the spex that the city had given her after she'd been woken from hibernation. Argyll had shown her how to use the navigation function, and its virtual display set a series of fat red arrows floating in the air that winked out one by one as, trailed by two drones, she followed them along a white gravel path between two-and three-storey apartment blocks with narrow gardens on set-back terraces and balconies hung with flowering vines or shaggy waterfalls of mosses and ferns. It was late in the evening. The panes of the dome polarised black, paths lit by tiny biolamps like green stars and a few dim street lights, and not many people about, for which Macy was thankful. She was dressed in a costume borrowed from Loris, baggy shorts and a pale blue T-shirt that hung to her knees, but most passers-by seemed to recognise her as she ankled along, and several stopped her to ask her how she liked their city, or simply to say hello.

The last of the red arrows winked out as she stepped onto the escalator that carried her down into the city's free zone. One of the drones that had followed her across the city angled away; the other, no doubt run by Speller Twain, parked itself in the air at the head of the escalator, vanishing from sight as Macy descended.

Everyone knew everyone else's business in the city. It was a small, crowded place, and as in all the city-states and settlements of the Outer System, which preserved democratic traditions long vanished on Earth, there was a custom of public candour and open access to surveillance systems and every kind of stored information. At least half the population posted unflinching details of their everyday lives on the net; everyone expressed opinions about anything and everything; anyone could attempt to gain any public position by participating in popularity contests, and the winners of those contests had to facilitate decisions arrived at through a combination of public debate and expert advice, and took part in regular question-and-answer sessions about their work. This tradition of open exchange of information was giving the construction crew all kinds of problems. Hundreds of people visited the biome every day. They picnicked on the main island, flew kites, watched the water level in the lake rise centimetre by centimetre, wandered in and out of labs and worksuites and pestered the crew with pointless questions about Earth and their work. Yesterday, while taking a short stroll along the rim road before supper, Macy had been accosted by an earnest young man who'd had plenty of ideas about what she was doing wrong. She'd only just been able to keep her temper while she countered his points one by one. Others were having a harder time dealing with the inexhaustible curiosity of the Outers; Cristine Quarrick had lashed out with considerable verbal inventiveness at a little girl who'd come up to her and asked her why she was so ugly, the girl had burst into tears, and everything had been caught by a passing drone and had nearly caused a diplomatic incident.

The city's free zone was the only place where its citizens had any privacy. There were no cameras in the free zone; nothing that accessed or fed into the net. All the city's ordinances, apart from those covering basic human rights, were suspended. After putting a data miner to work in the records of the city's camera system, Argyll had discovered that Ursula Freye visited the zone each and every day. Usually she spent an hour or two there before returning to the biome, although sometimes she came out only a few minutes after she'd gone in, and once she'd stayed the night. No wonder Loc Ifrahim had been so vague when Macy had asked him who Ursula had been talking to; no wonder he and Speller Twain were so anxious to put a stop to it. Ursula had found the one place where no one could spy on her. Where the citizens would respect her privacy. Where Macy would have to go if she wanted to find out what the woman was up to, who she met with, what she talked about.

Macy had escaped from the Church of the Divine Regression and survived the gangs and cops in the slums of Pittsburgh, as well as numerous encounters with wildsiders and bandits in the borderlands: she was pretty sure that she could play this situation and come out in front. Even so, she felt a flutter of apprehension as she rode the escalator down into the free zone. She really hoped that this didn't have anything to do with Ursula Freye's determination to root out the truth about Manny Vargos's death, that Ursula was visiting the zone because she was looking for something clean and simple like sex or drugs, some release from her unreasoning grief.

It was always night, down there in the zone. A broad avenue followed the curve of the tent's coping wall, intermittently illuminated by multicoloured holos and neon. There were people wearing body-enveloping cloaks and masks, people wearing nothing but morph paint, patterns and images drifting across their bare skins like clouds, but most were dressed in the colourful tatterdemalion clothing that passed for everyday wear in the city. Short backless jackets like yokes, jackets with rubber spikes or armoured plates, jackets patched from feathers or fur, ruched and intricately pleated shirts and cut-off kimonos that shimmered like water or mercury, kilts, baggy shorts, tights with ridiculous codpieces, plain shifts . . .

Some of them, recognising Macy and surprised to see her there, broke protocol and stared openly. She stared right back. She didn't feel in the least bit intimidated. Compared to the brawling streets of Pittsburgh, the zone seemed as artificial and safe as a children's playground. She passed body-mod shops, wireshops, smokehouses, meat markets where citizens bought or sold or gave away all kinds of sex. Even on the main drag, at least half the places were no more than recessed doors that gave away nothing about what went on inside. Others stood under gaudy and elaborate signs. The Gilded Palace of Sin. Fight Club. Lies, Inc. There were vanilla bars and restaurants, too. Macy hit those first, found Ursula Freye in the third place she checked out, a bar that called itself Jack Frost.

The name glowed red inside a holo of a melting block of ice hung above a narrow doorway. Macy followed two men into a passage hung with fur coats. They had to be artificial, cultured or machine-made, but the sight of them hanging in dense rows gave Macy a little shock. She had to swallow her queasiness before she could emulate the men she'd followed and pull on one of the soft, heavy furs and push through the rest into a dimly-lit cave.

It was freezing cold, covered in ice. A floor of rough black ice, booths and tables carved from ice dyed different shades of red, ribbed ice walls and a low ceiling supported by columns of fused giant icicles in which scattered lights shone like dim, frozen stars. Tinkling music hung in the air, delicate as smoke. Robots shaped like squashed crabs crawled over the ceiling and around and about the icicles, taking orders, scurrying off, returning to lower with whiplike tentacles drinks and tiny plates of food to table tops. The decor and dim lighting confused the transition between the interior and video windows displaying views of the moonscape outside the city.

It was only the second time that Macy had seen the surface of Callisto. She stepped towards one of the windows and its view of a cratered plain stretched to a horizon curved sharp and clean against a black sky where Jupiter's banded disc hung like a marvellously detailed brooch, didn't notice Ursula Freye until the woman walked towards her through the cone of light cast by the old-fashioned lamp post (exactly like one Macy had once seen in the preserved section of Pittsburgh) that stood in a continuous flurry of snow at the centre of the bar.