'That's for you to find out,' Speller Twain said. 'Eight o'clock, wasn't it?

And at the usual place. Unless you two have been having meetings I don't know about, that's the bar down in the free zone. If you're going to do this, I think you'd better get a move on. You don't want to be late, do you?'

8.

Macy rode a tram into Rainbow Bridge, got on another tram and rode across the city, and took the escalator down into the free zone, floating on a mixture of anger and anxiety. As she moved through shadows and neon glow towards the bar, Jack Frost, passing people dressed for every kind of carnival, a tall figure wrapped in a red cloak and wearing a fox mask stepped out of a passageway and caught her arm and said, 'She isn't there.'

Macy shook off the figure's grip. 'This isn't any business of yours, so how about you back right off?'

The fox-faced figure regarded her for a moment, amber eyes gleaming above the auburn and white muzzle and the crooked sharp-toothed grin, then reached up and swept off the mask. 'I don't want to see you hurt,' Loris said.

Macy's anger surged over her spark of surprise. 'You've been spying on me.'

'Ursula Freye isn't waiting for you in Jack Frost,' Loris said. 'She's still in the biome. Speller Twain intercepted her before she could leave. I can't be sure, but I think he's interrogating her.'

'Bullshit. He sent me here to try to talk some sense to her.'

'No,' Loris said. 'He told you that he wanted you to find out what Ursula claims to have discovered. But it's clear that he and Loc Ifrahim have other plans. They've sent you here because they want to use you in some way, Macy. They want to set you up. To make sure that you take the blame for whatever it is they are planning to do.'

'Bullshit,' Macy said again, but with much less force this time, her anxiety fed by Loris's calm green gaze.

'Many people want the biome project to fail,' Loris said. 'People in my city and elsewhere in the Outer System. People in Greater Brazil; people working for the construction crew. Mr Twain. Mr Ifrahim.'

'So you believe Ursula's fantasy.'

'It may not be a fantasy.'

'She's hurt. All torn up by Manny's death. Grieving. It's driven her a little crazy, and she's trying to justify an accident with some fantasy about murder and conspiracy. You encouraged that, for whatever twisted reason, and now you're trying to drag me into it too. No way,' Macy said, and pushed past Loris, heading towards Jack Frost's little sign, glimmering silver and red amongst the shoal of holos and old-fashioned neon signage that swam in the artificial twilight of the free zone's broad avenue.

Loris matched her bounding stride, saying, 'Is the problem with the Skeletonema cultures a fantasy?'

'We found what was wrong with them and we fixed it. And it wasn't sabotage.'

'No, you didn't,' Loris said. 'The phosphate problem was a side effect. Listen to me, Macy. Listen carefully. We checked every species your crew brought here, a simple and obvious precautionary measure. And we found two novel sequences in the Skeletonema's genome. One is at the tip of chromosome four, a repetitive pattern of base pairs substituted for the telomeric sequence that usually caps the chromosome. A clock sequence. The other codes for six genes on the same chromosome, and is inserted next to a gene that produces one of the proteins that controls phosphate uptake. The clock sequence shortens by a single base pair at every round of cell division. And when it has shortened to half its original length it activates transcription of the second sequence. And that will produce a pathogenic RNA viroid, some six to eight weeks after the lake is seeded with Skeletonema culture at the opening ceremony. The Skeletonema population will crash, and bacteria feeding on all that dead biomass will use up all the free oxygen in the lake and wreck its ecosystem. Put on your spex. I'll show you the genomic analysis-'

'I'm sure you can show me just about anything you want,' Macy said, and went through Jack Frost's narrow doorway and barged through the heavy fur coats hung in the corridor, out onto the ice floor of the dimly lit bar.

'You can see that I was telling the truth about Ursula,' Loris said, after Macy had stalked around the bar and checked every booth.

'How do I know you didn't kidnap her?'

'Have I kidnapped you?' Loris said. 'Listen to me, just for a minute. We think that we were supposed to find the sabotage to the Skeletonema cultures. We made no secret about checking the species sent from Earth. And if the deleterious effect of the inserted sequence on phosphate transport was a mistake, it was a very clumsy mistake. Someone wants to show that they could reach out and hurt the project. Perhaps they want to cause a scandal. Or perhaps they want to divert attention from something else.'

Macy said, 'Did Ursula find something?'

'I don't know.'

'Was Manny Vargo murdered?'

'You and Ursula may be in grave danger, Macy,' Loris said. 'It may be too late to help Ursula, but I know that I can help you. Stay here. Don't go back to the biome.'

'Or what? You'll arrest me?'

'Of course not. But it really would be a good idea if you stayed here until we found out what Mr Twain is planning.'

'I don't aim to be a part of anyone's plans,' Macy said.

She left the bar and broke into a run. Down the long curve of the free zone, up the escalator, along grass-floored streets. She jumped onto a tram and stood at the back, catching her breath, watching apartment buildings flow past on either side. No one seemed to be following her; not even a drone.

She was more frightened than angry now, trying to stay calm, trying to think things through. One thing she knew: Speller Twain couldn't touch Ursula Freye. He could question her and threaten her, but he couldn't hurt her, and Loc Ifrahim couldn't hurt her either. Ursula would survive this, she could protect Macy if she wanted to, and she'd definitely want to protect Macy if she had some evidence of sabotage. So the first thing Macy needed to do was check out the Skeletonema cultures and sequence the diatom's genome.

She wondered why Cristine Quarrick hadn't spotted the clock sequence and the viroid genes, and had the chilly thought that perhaps Cristine already knew about them. That she was in on the conspiracy, too. Yeah, or maybe Cristine was just lazy or too busy. Or maybe Loris had made up the whole story, so there was nothing to find. You could get lost in a hundred different ways if you started to speculate. Stick to facts. Sequence the diatom genome. Look for those inserted genes. Find Ursula. Take it from there.

No one stopped Macy when she changed trams and rode into the biome; no one stopped her when she came out of the station at the main island. Night. Every pane of the tent polarised to black and the chandeliers turned down to a faint glow like tarnished starlight. Lights along the edge of the island glimmered above their slurred reflections in the lake. A faint nimbus enveloped the skeleton of the half-constructed island inside the coffer dam, throwing the magnified shadows of the robots working inside it across a slanting portion of the tent's roof.

A drone began to follow Macy as she left the station. She gave it a hard stare to let whoever was driving it - Speller Twain, Loris, some innocent busybody - that she knew that she was being watched, and walked on, determined not to look at it again, a tingling itch between her shoulder blades.

She hurried along the path that cut through the wooded ridge down the centre of the island, began to cross the slender bridge that linked the island with the eastern rim road - and all the lights went out. The little lights marking the bridge's footway, the chandeliers' glow, the spiderweb of lights hitched across the island, the lights around the station entrance and the crew's living quarters. Only the construction site was still lit.

Macy flinched when something softly splashed into the water below the bridge. She found her spex and put them on and dialled up the light-enhancement function, saw the fat cigar of a drone, presumably the one that had been following her, floating on the black wash. Something had knocked out the lights, the drones ... A bad feeling rose up in her, thick as nausea. She felt horribly exposed, up there at the apex of the bridge's high curve, and she ran down its far side and ran straight across the rim road into the strip of parkland beyond, bounding light as a bird through the luminous dark, twisting this way and that to avoid clumps of flowering bushes and outcrops of rock, almost laughing out loud when, trying to halt her headlong flight, she pitched head over heels into a patch of oleander, rolling to a breathless halt amongst a tangle of scratchy branches and leaves, a snowstorm of waxy petals drifting around her.

She lay there for a little while, staring up at the black roof and listening with fierce attention. The whines and thumps of the robots working inside the luminous cup of the coffer dam; the reaction motor of a boat fading away somewhere on the lake; voices drifting across from the island, people calling out, asking each other what was going on. When she was as certain as she could be that no one was following her, Macy got to her feet and went on through the park, moving parallel to the rim road, slowing as she approached the huge shadow of the support strut. She drifted to the first of the bioreactors in the plaza under the arch of the strut, laid a hand on its warm flank and felt the reassuring purr of its pumps. The backup supply had kicked in, so she didn't have to worry about a mass die-off of her precious cultures. She threaded her way between the tanks, stopped.

Something sprawled on the grassy space in front of the entrance to the lab. It was a body. It was Ursula Freye.

She lay on her back, one arm carelessly flung out as if reaching for something, head turned sideways. She didn't move as Macy crept towards her, softly calling her name. Her nostrils were wet with blood and blood had run in a thick line down her left cheek. Her eyes were open but rolled back. Macy pressed two fingers under the hinge of her jaw, failed to find a pulse, and with a flash of freezing fear realised that Loris had been right all along. She'd been set up. She sprang to her feet so quickly that she left the ground for a couple of breathless seconds; as she floated down the string of chandeliers hung above the lake lit up bright as noon.

Even though the light-enhancing function of Macy's spex immediately cut off, she was dazzled by the sudden flood of brightness. She tore off the spex and thumbed tears from her eyes, saw a shadow race at her from the right, someone running too fast, losing his footing and plunging headlong. It was Speller Twain, bouncing up and aiming a taser at her, the kind that shot fractally compressed loops of superconducting nanowire.

Macy jinked left as a miniature lightning bolt scorched across the turf in front of her. Speller Twain shouted, ordering her to stop, but she was already running, bounding across the lawn like a gazelle pursued by a lion. A chain of bright sparks spattered the side of a bioreactor as she flew past, and she jumped high and caught the rim and pulled herself up, moving easily and fluidly in the low gravity. She ran the length of the boxcar-sized tank, jumped the wide gap to the next, ran along that and jumped to the ground and ran on across the plaza. Sparks exploded from the railing at the edge of the plaza as she hurdled it, spattering her with stinging flecks of hot metal, and she dropped straight down and ran down the gentle slope of the dry lake bed towards the beached skiff.

She was dragging the skiff into the water when Speller Twain vaulted the railing. He landed awkwardly and went over on his back, and his taser spat a bolt that shot straight up through the bright air and burst like a firework on a pane of the tent high above. As the big man got to his feet, Macy saw something move out across the railing above and behind him, saw him whirl around as the drone stooped down at full speed and slammed into his face.

He fell down again, and dropped the taser. Macy rushed forward and scooped it up, dancing away when Speller Twain made a swipe at her. She stepped backward towards the skiff, keeping the taser on him. He pushed to his feet and spat a mouthful of blood and told her that she was making a big mistake.

Macy was knee-deep in water. Her mouth was dry and she had to suck up some spit before she could say, 'Stay right there, Mr Twain. I don't want to shoot you.'

'You aren't going to shoot me,' Speller Twain said, and flew at her.

She shot him. The bolt struck his chest and he belly-flopped into the water, jerking and flailing. Macy scrambled into the skiff and pressed the button that started its motor and jammed the tiller hard around, spinning the little craft through a hundred and eighty degrees as it accelerated away. She'd drawn a long arc past the mouth of the bay before she'd calmed down enough to realise that there was only one place where she could go now. She turned west, heading for the far shore, and activated the phone function of her spex. But before she could place the call, a window scrolled down and Loc Ifrahim leaned into her face and said, 'Now you've gone and done it.'

Macy tore off the spex and threw them out across the water as hard as she could, ran the skiff onto the dry lake floor at the foot of a set of stairs, swarmed up them to a broad promenade that ran in front of a low block of terraced apartments. She paused then, breathing hard, looking back across the lake. Her heart was banging madly in her chest. It was only ten minutes since she'd discovered Ursula's body.

A star flared in the middle air: chandelier light glancing off a drone that was dropping towards her.

Macy dodged around stacks of construction materials, charged through the broad entrance of the apartment block, lost her footing and flew across an atrium. She slammed against a wall and sat down hard, breath knocked out of her, pain in her left ankle. The drone drifted down a slanting shaft of light that speared through a round unglazed window and a stentorian voice shivered the air, calling her name, telling her to stay where she was. Macy raised the taser and took careful aim, but her hand was trembling badly and her first shot missed, howling away through the window. The drone jerked sideways, and Macy's second shot struck it in a shower of sparks that ruptured its helium-filled bag.

As it tumbled out of the air, she jumped up and took off, limping on her wrenched ankle, out through the far side of the atrium into a courtyard. Bamboos and giant jade-green cushions of mosses, raked black sand, the dry bowl of a black stone fountain. Macy plunged through an archway beyond. Stairs to her right wound to the upper storeys; stairs to her left dropped to the basement.

She knew from briefings that every building in the city had a basement passageway leading to emergency shelters and airlocks, in case there was a catastrophic failure of the integrity of one or more of the tents and domes. The Outers, who for more than a century had been living in an environment that would kill them in an instant if they made a single misstep, were very big on safety and emergency planning. Macy was betting her life on that caution now, hoping that even though the apartment building hadn't been finished its airlock would be functional. If it wasn't, she probably wouldn't have enough time to find another way out of the tent before Loc Ifrahim caught up with her.

The door at the bottom of the stairs was shut and nothing happened when Macy punched the big red button that was supposed to unlock it. She spent a panicky minute spinning the wheel that worked the ponderous manual mechanism, opening the door just wide enough so that she could slip inside, and then she had to turn another wheel to close it.

A narrow corridor sloped away, lit by dim lights embedded in the floor. She cannoned off its walls as she ran down it. Her ankle was hurting badly now, but she couldn't slow down. Loc Ifrahim would soon work out where she was going, and if he could turn the chandeliers off and on at will he might well have the ability to lock down the tent's emergency exits too . . .

The corridor went down a long way. The air grew colder. Her breath puffed out in little clouds; frost sparkled on the walls. There was another door; again, she had to turn a wheel to open it. Lights came on beyond, revealing a low-ceilinged bunker. During an emergency, citizens who weren't certified for rescue and repair work were supposed to hunker down in places like this until it was safe to return to their homes. The memory-plastic floor could grow seats or beds; a medical pod stood in one corner like an old-fashioned cabinet freezer; there was a tiny kitchenette and a pair of shower/toilets, crates of freeze-dried food and clothing and blankets. And there was also a ladder leading up into a shaft signposted with a cartoon of a round door emitting a little cloud: the universal sign for an airlock.

Macy hauled herself hand over hand up the long shaft and emerged into a small brightly lit antechamber where two dressing frames stood either side of a steel door. In a jittery rush, she stripped off her coveralls, pulled on a one-piece thermal liner, and stepped into the smallest of the bright red pressure suits that hung in the dressing frames. She pulled up the big double zip, used the concertina joints above elbows and knees to adjust the fit, fingers stiff and clumsy inside the suit's heavy gloves, shrugged into the harness of the lifepack, lowered the fishbowl helmet and latched it tight. A HUD lit up inside the faceplate and Macy stepped away from the frame and clumped into the airlock and started its cycle. Mist condensed around her and was whisked away as the air was evacuated, the outer door swung open, and she stepped out onto the surface of Callisto.

It was late afternoon. The sun, much shrunken but still the brightest object in the black sky, burned low in the west. Jupiter's exotically banded disc, a little over half full, hung high overhead. The airlock was housed in a blister that stood at the edge of a broad dusty apron marked everywhere with bootprints. Behind it, the flank of the biome's tent rose at a steep angle, a gigantic jigsaw of black panes and tension bars set between struts as sturdy and tall as skyscrapers. In every other direction cratered terrain stretched to a curved horizon just three kilometres away.

The pressure suit's navigation system highlighted and tagged features scattered across the stark moonscape. A flat-topped hill at the horizon to the northwest was the rim of Wealtheow Crater, with a vacuum-organism farm spread in front of it. A line of construction robots parked in the shadow of a long, low berm two klicks away. A couple of utility shacks. And a silvery roadway that cut past the edge of the apron and swung around the tent that housed the biome. According to the navigation system, the road led straight to the city. It was a hike of some ten klicks that even in Callisto's low gravity would take Macy more than an hour - assuming she could manage to travel that far in the bulky pressure suit, with a sprained ankle. But she couldn't stay here. Speller Twain and Loc Ifrahim would soon figure out where she'd gone, and they couldn't let her escape.

Stepping through three layers of increasingly graphic warnings, Macy turned off the pressure suit's beacon, then started towards the distant line of construction robots. She was possessed by the same airy mixture of excitement, dread, and determination she'd felt when she'd escaped from the Church of the Divine Regression. Back then, she'd spent a year planning her escape. She'd accumulated and hidden a cache of supplies and a change of clothes at the perimeter, memorised three different routes to the nearest highway, written a worm that would shut down the security AI, stolen tranquillisers from the pharmacy to drug the guard dogs, prepared and rehearsed every step of her escape. But this time she was making it up as she went along.

She was close to the long row of construction robots now, heading towards a small bulldozer with a moulded seat elevated behind its broad blade. All she had to do was figure out how to start it up, and she could ride into the city in style . . .

An icon started winking in the virtual display that ghosted her vision: an incoming call on one of the short-range channels. She turned, felt a panicky rush of adrenalin when she saw a figure in a red pressure suit just like hers walking away from the airlock on the far side of the swale of tracked dust, shuffling as cautiously as an old man crossing an ice rink. She dodged between two of the big machines and doubled back on her tracks and found cover in the stark black shadow cast by a mesh wheel three metres high.

The figure was coming on, small and vivid against the dark ground, heading straight towards her. She patted the pouches and clips of her suit's utility belt, and had a clear picture of the taser lying on the floor by the dressing frame. Dumb, Macy, real dumb. Almost as bad as forgetting to jam the airlock. The icon was still winking. Well, the son of a bitch already knew where she was: if she answered his call, she'd at least know who she was dealing with.

'There you are,' Loc Ifrahim said when she opened the channel.

'Listen, Macy, I'm here to help you. Stay calm and don't do anything stupid. We can clear this up, just you and me.'

'How are we going to do that?'

Macy was certain that Loc Ifrahim and Speller Twain had been planning to frame her for the murder of poor Ursula Freye. She'd ruined their plan by managing to get away, so now they had to kill her. If they didn't, if she fell into the hands of the city's peace officers, she'd blow their little plot wide open. She began to move towards the biggest of the construction robots, a crane mounted between three pairs of wide caterpillar tracks. She'd seen plenty of big equipment during her service with the R&R Corps, but this was a true monster. Its platform was at least fifty metres long and its telescopic jib, woven from skinny struts of fullerene composite and canted at a thirty-degree angle, was at least twice as long.

'We need to sit down together and get our stories straight,' Loc Ifrahim said. 'To begin with, I need to know what happened between you and Ursula.'

'She was dead when I found her. You should know that.'

'All I know is that Mr Twain found you by her body. You attacked him, and then you ran away. It doesn't look good, does it? But I'm willing to hear your side of the story. I'm willing to sit down with you and work out what you have to do.'

'I know one thing. Ursula was right. Someone is trying to sabotage the biome,' Macy said, and cut the link.

She thought about calling Loris, but she didn't know how long it would take help to arrive. Or she could make a run for it, climb the steep side of the berm, head out across country. She had enough air and power to survive out here for more than two days, but she wouldn't be able to travel fast on her damaged ankle, and if Loc Ifrahim knew how to drive one of the construction robots he could easily chase her down. No, she thought, she was going to have to tackle him herself, right here, right now.

Macy stepped back from the shadow cast by the crane, then ran forward, pain spearing her left leg from ankle to knee at every other step, and jumped to the top of one of its broad tracks. She landed awkwardly, had to grab at the link between two plates of the track to stop herself rebounding. She lay there for a few moments, dazed and out of breath, then crawled to the end of the track. She was five metres above the ground, could see Loc Ifrahim moving along the line of construction robots, flitting from shadow to shadow, turning this way and that, aiming the taser at likely hiding places. Even when he paused in the deep black shadows she could see him clearly in infrared; the insulation and the heat-recycling system of his pressure suit weren't entirely efficient and he burned white as a ghost, more than eighty degrees hotter than his frigid surroundings.

If he glanced up she'd be finished, but he was too busy looking under the frames of robots, looking behind wheels and tracks . . . Macy crawled backward, stayed absolutely still and let ten minutes pass before she risked taking another peek. At first she couldn't spot him, but then she turned and saw that he was creeping past the far end of the crane, stooping to examine the shadows underneath it like a man searching for a lost pet. She pushed up and bounded down the length of the track and launched herself in a long, floating parabola and smashed into him and knocked him to the ground. He tried to rear up, but she grabbed his helmet in both hands and thumped it into dust soft and gritty as sugar, then opened the line-of-sight channel and asked him if he wanted to live.

'If you kill me, you'll die too, and not in a nice way,' he said. 'They expose murderers to vacuum.'

'That's what I'll do to you if you don't keep still,' Macy said and cut the channel. She was tired and in a lot of pain from her ankle. She didn't need to hear any more of his bullshit.

She couldn't find the taser - he must have dropped it when she'd knocked him down - but there was a plasticuff loop strung on his utility belt. She used it to fasten his arms behind his back, then pulled down the city's directory and made a phone call.

Loris answered at once, and asked Macy if she was all right.

'I want to thank you for knocking Mr Twain down with that drone. That was you, right?'

'You didn't have to run, Macy. I know how you were set up. I was coming to help you.'

'Do you know that Mr Ifrahim came after me too? Luckily, I got the jump on him. In fact, I'm sitting on him right now. You can question him-'

'No, we can't. He has diplomatic immunity. What we can do is bring you in. Where are you?'

'If you let him go, he'll no doubt claim that Ursula and me were plotting all kinds of sabotage. Including the Skeletonema cultures, which are my responsibility after all. We had a falling-out, and I killed her. And I bet Twain and Ifrahim could make a good case that I murdered Manny Vargo too. Because he discovered that the wrong culture had been loaded.'

'Or simply because his death would also damage the project,' Loris said. 'We don't know everything, Macy. Perhaps we never will. But we do know that you are an innocent party caught in the middle of it all. That's why we are willing to offer you protection.'

Macy realised that she had been used to flush out Speller Twain and Loc Ifrahim. Set up. Staked out like a wildsider sacrifice. She said, 'I really have been played by both sides, haven't I?'

'We are grateful for your help,' Loris said. 'I want you to know that you're not in as much trouble as you think you are.'

'I know I can't go back to the crew, that's for sure. There's a bunch of construction robots parked outside the western flank of the dome. You can find me there.'

'I'll be there right away,' Loris said. 'Don't worry, Macy, you've made the right choice.'

Macy spotted the taser lying in the dust and pushed away from Loc Ifrahim and snatched it up. Loc Ifrahim rolled over and tried to sit up, subsided when she waved the taser at him. The icon of the line-of-sight channel started blinking again, but she ignored it. She had nothing more to say to the diplomat.

A few minutes later, the pressure suit's navigation system alerted her to the approach of a vehicle and bracketed a bright dot that slid low across the black sky. It quickly resolved into a single figure in a pressure suit riding a platform on top of a compass rose of thrusters. Loc Ifrahim sat up. Macy ignored him, watching as the platform came in, thrusters blinking as they made minute adjustments to its pitch, drifting low towards her, kicking up dust, settling on spidery legs.

Macy waved to it, remembering her breathless anticipation years ago on the dark road that cut through Nebraska's night, when she'd swung into the cab of the road train she'd flagged down and the driver had turned to her. A chunky woman with a blond crew cut and a pitted complexion, asking her where she wanted to go. And she'd said, with the bold naivety forgiven only in the young, 'Anywhere else.'

On the platform, the figure in the pressure suit raised one hand, then touched its helmet.

Macy had already walked away from one life; now she was about to do it again. She switched on the short-range channel and said to Loc Ifrahim, 'You can tell Mr Peixoto that I quit.'

And that was it: she was a refugee.

9.