"Still here..." Momentarily, her voice broke up into staccato shards, as if they were hearing pieces of her

message out of sequence. "...but you might want to cast off sooner rather than later. Conditions are getting seriously sub-optimal."

"Shouldn't we wait things out?" Auger asked.

"You'll be relatively safe once you clear the throat."

"Why does she not fill me with confidence?" Floyd asked.

"Never mind," Auger said. "Robot: you got that injection sequence ready?"

The piping voice of the machine a.s.sured her that all was ready. "Throat stability is locally optimal," it

said, whatever that meant.

"You buckled in, Floyd?"

"I'm ready."

"There'll be quite a kick. Be prepared." Then she raised her voice. "OK, robot, inject us whenever you

want."

"Injection in five seconds," the machine said.

Ahead, the iris cranked open. Floyd narrowed his eyes against the intense, roiling glare that spilled between the opening blades. The light flowed in strange, sicklelike patterns down the mirrored shaft. From somewhere behind the ship, the mechanical sounds intensified, and he heard a sequence of thuds and clunks like some enormous clock gearing itself up to chime.

"Three seconds," the robot said. "Two. One. Injecting."

Floyd's bruised spine yelled a protestation into his brain. He felt as if a family of gorillas was practising xylophone exercises on his vertebrae. He started to say something, some useless moan of animal discomfort, and then found that he did not have the strength to speak; even his lungs felt as if they were being squeezed like bellows. His head and neck mashed back into the seat restraints and he felt a mouthful of drool spill down his chin. His vision darkened around a central core of brightness.

They were moving.

They were moving so quickly that they were not even in the chamber any more. They had already traversed the gla.s.s shaft and the mirror-lined part of the tunnel and were speeding through the heart of the opening iris, into the unimaginable fury of the light beyond.

That was when it got really b.u.mpy.

The pressure forcing him into the back of the seat had abated and in its place was a dreamy lightness-ofstomach feeling, as if they were falling, but the ship was now lurching from side to side, each violent movement accompanied by a tooth-grinding rattle of ravaged metal. This, Floyd thought, was how it felt to grind past an iceberg in an ocean liner. He imagined scabs of the ship's hull breaking off into the bright inferno of whatever it was they were flying through.

He didn't think it very likely that it was a tunnel under Paris any more. Or even a tunnel under the Atlantic Ocean.

"I'm closing the shields now," Auger said. "The view doesn't help much. Especially not after ten hours of it."

She touched a control above her head, using her good arm, and iron eyelids snicked down over the windows. Interior lights came on, bathing everything in a low-key glow. Floyd watched the grid pattern, his hand ready to close around the joystick.

"I'll look after it for now," Auger said, taking hold of a similar control on her side of the cabin. "You can watch and learn."

"There are a couple of questions I really need to ask," Floyd said.

"OK," Auger said. "I guess you've earned them."

"Where is this tunnel taking us?"

"It's taking us to Mars," Auger said. "Specifically to Phobos, one of Mars's two natural moons."

"So it wasn't a codeword after all."

"No," she said.

"I figured that part out, for what it's worth. I also decided that I don't think you're a Martian."

"No, I'm not."

"But you're not from Dakota, either."

"No, Dakota was a lie. But I am from the United States." She offered him a nervous smile. "Just not the

one you were thinking of, although I suppose you could call them distant political relatives."

"And your name?"

"That bit was true. My name's Verity Auger, and I am a citizen of the United States of Near Earth. I'm a

researcher for the Antiquities Board. I was born in the orbital community of Tanglewood in the year

twenty-two thirty-one. I'm thirty-five and divorced, with two kids I don't see as often as I should." "The odd thing is," Floyd said, "I don't doubt you for a moment. I mean, what other explanation could there be?"

"You seem very relaxed about it," she said.

"Given all that I've seen, the only possible explanation is that you're a time traveller."

"Ah," Auger said. "That's the problem, you see. I mean, time travel is definitely involved here, but not

in quite the way you're thinking."

"It isn't?"

"No. But you're half-right. You see, one of the two people in this ship is a time traveller. And it isn't

me. Do you want me to carry on?"

"I thought I had you figured out for a moment," Floyd said.

"One step at a time," Auger told him. Then there was a shriek from some part of the instrument panel and a dozen red lights started flashing in synchronisation. Auger bit her lip and pushed her joystick to one side. Floyd felt the ship veer: a sickening feeling like a car hitting ice.

"Was that a...what did she call it? Smash?"

"That was a software crash, yes," Auger said. She flipped a bank of switches, then threw back a gla.s.s cover to press a large red b.u.t.ton. "And this is the reboot sequence, so pay attention."

"We've only just left."

"I know," she said. "We've got thirty more hours of this to get through. I think the ride home is going to be a lot more interesting than I was hoping."

TWENTY-EIGHT.

They had been under way for six hours. The guidance system had failed two or three times an hour initially, but lately the ride had become lullingly smooth, with only the occasional stomach-churning veer or swerve. They had eaten a light snack of pre-packed rations (the food was tucked into unmarked foil pouches that, to Floyd's obvious delight and fascination, warmed the food automatically when they were opened) and Floyd had explored the tiny, intimate microcosm of the toilet, with its daunting methods of collecting bodily waste under weightless conditions. Auger had asked him if he felt any motion sickness, and he had replied truthfully that he felt none.

"Good," she said, popping a dark pill into her mouth. "It must be all that time you spent at sea. Good practice for a trip down a wormhole, even though you probably didn't realise it at the time."

"Are you feeling ill?" he asked.

"Apart from the fact that I've got a bullet lodged in my body that the robot thinks might kill me? No. I've never felt better."

"I meant the pill."

"It's UR," she answered, as if that explained everything. When Floyd just stared at her, she said, "Universal restorative. General-purpose medicine. It will heal anything, cure any ill. It'll even keep you alive for ever."

"Then you're immortal?" he said.

"No, of course not," Auger said, as if the very idea embarra.s.sed her. "If I took one of these every day- or every week, or however often it is you have to take them-then I might be, I suppose. At least until the supply ran out, or I got some disease so fascinatingly exotic that even the UR couldn't fix it. But there isn't enough UR in the whole system for me to take it all the time, and in any case, my people don't agree with it."

"You don't agree with medicine that makes you immortal?" he asked, a little surprised by her statement.

"There's more to it than that. My side-the USNE, the Threshers, call us what you will-doesn't have the means to make UR. What UR we do have access to is supplied in very small, expensive and controlled quant.i.ties by our moderate allies in the Polities."

"Haven't you tried making it yourselves?"

She popped another pill from the cylindrical dispenser and held it up for Floyd's inspection. It looked no more impressive than a discarded b.u.t.ton, or a nub of dark clay. "We couldn't make it even if we knew the recipe. The technology embedded in this pill is one that we've chosen to reject." With particular care, she returned the pill to its canister. "Except, of course, when we really need it, which tends to be on high-risk operations like this. So call us screaming hypocrites, and see if we care."

"What's so dangerous about a technology used to make pills?"

"The technology is a lot broader in its applications," Auger said. "That isn't really a pill. It's a solid ma.s.s composed of billions of tiny machines, smaller than the eye can see. You wouldn't even see them under a microscope. But they're real, and they're the most dangerous thing in the world."

"And yet they can heal you?"

"They swim into your body after you've swallowed the pill. They're smart enough to identify what's wrong with you, and adept enough to put it right. The bodies of the Slashers are already swarming with tiny immortal machines. They don't even need UR, since nothing ever goes wrong with them."

"Can't you be like that?"

"We could, if we wanted to. But a long time ago something bad happened that convinced us that the Slashers were wrong, or at least foolhardy, to embrace that technology so wholeheartedly. It wasn't just..." and then she said something that sounded worryingly close to "banana technology," but which Floyd a.s.sumed-hoped, for the sake of his sanity-he'd misheard.

"Not just that," she continued. "But virtual reality, radical genetic engineering, neural reshaping and the digital manipulation of data. We rejected all that. We even established a high-level quasi-governmental organisation-the Threshold Committee-to keep us back from the brink of ever developing any of those lethal toys by accident. We wanted to stay on the cusp, the threshold, but never quite cross it. The Slashers call us Threshers. It's intended as an insult, but we're quite happy to apply it to ourselves."

"This bad thing that happened," Floyd said. "What was it?"

"We destroyed the Earth," Auger said.

"That'll do it."

"The thing is, Floyd, it didn't have to happen the way it did. If we allowed your world to run forward in time from the present, maybe we'd never end up with what happened in twenty seventy-seven...and everything would be different now. Not necessarily better, but different."

"I'm not following you."

"You and I don't share the same history, Floyd. After nineteen forty, there's nothing in common between our two worlds."

"What's the significance of nineteen forty?"

"That's the year when Germany attempted to invade France. In your timeline, the invading forces ground to a halt in the Ardennes, becoming sitting ducks waiting for the Allied planes to bomb them into the mud. The war was over by the end of the year."

"And in your timeline?"

"The invasion was a staggering success. By the end of nineteen forty, there were very few places in Europe and North Africa that the German army hadn't occupied. By the end of nineteen forty-one, the j.a.panese had joined forces with the n.a.z.is. They launched a surprise attack on America, turning the whole thing into a global conflict. It was mechanized warfare on a scale the world had never seen before. It's what we call the Second World War."

"You don't say."

"It lasted until nineteen forty-five. The allies won, but the cost was considerable. By the time the war was over, the world was a completely different place. We'd let too many genies out of too many bottles."

"Such as?"

"I don't even know where to begin," Auger said. "The Germans developed high-alt.i.tude rockets to bomb London. Within a couple of decades, the same technology would put people on the Moon. The Americans developed atomic bombs that were used to flatten j.a.panese cities in a single strike. Within a couple of decades, those bombs had become powerful enough to wipe out humanity many times over, in less time than it takes you to make breakfast. Then there were the computers. You've seen the Enigma machines. They played a significant role in wartime cryptography. But the allies built bigger, faster machines to crack the Enigma messages. Those machines filled entire rooms and drank enough power to light up an office block. But they became smaller and faster: much smaller and much faster. They shrank down to the point where you could barely see them. Valves became transistors, transistors became integrated circuits, integrated circuits became microprocessors and microprocessors became quantum optic processors...and still it s...o...b..lled. Within a few decades, there was no aspect of living that hadn't been touched by computers. They were everywhere, so ubiquitous that you almost didn't notice them any more. They were in our homes, in our animals, in our money, even in our bodies. And even that was just the beginning. Because by the beginning of the new century, some people were not content with just having very small machines that could process a lot of data very quickly. They wanted very small machines that could process matter itself: move it around, organise and reorganise it on a microscopic scale."

"Why do I have the impression that this wasn't necessarily a good thing?" Floyd asked.

"Because it wasn't. Oh, the idea was sound, and the tiny machines did a lot of good in many areas of human life. UR was on the good side of the equation. The trouble is, when you're dealing with what is in essence a new form of life, there simply isn't room to make too many mistakes."