"Not much. Clothes. Paper. Simple tools, like spades and screwdrivers. Basically anything it deems safe.

We actually managed to fool it, once, but in a very trivial way. It won't let a gun through, not even a replica of a twentieth-century weapon. But we were able to dismantle a weapon and smuggle through its component parts-that worked. But what was the point? It's easier to find a real gun on E2."

Auger reached out towards the beguiling yellow surface. "Can I touch it?"

"h.e.l.l, yes. You can put your hand through it. Going to have to put your whole body through it anyway, so there's no harm."

Auger pushed her finger towards the eerie yellow membrane. It took longer than she had expected for her finger to encounter any surface. Then she felt a p.r.i.c.kle of sensation in the very tip. She pushed harder, and the yellow surface began to visibly deform, puckering inwards from the point of contact. She was reminded of surface tension on water, the way it formed a skin that resisted gentle pressure. A rust-brown discoloration appeared in the yellow, radiating away from her finger in a concentric pattern.

"Are you absolutely sure this is safe?" she asked again.

"We've all been through it hundreds of times," Skellsgard said. "Bodies aren't a problem. It discriminates between complex biological processes and nanotech pretty well."

"Pretty well?"

"Just push."

Auger increased her pressure. There was a snapping sensation and suddenly her hand was engulfed in yellow up to the wrist. The surface had flattened itself again around her limb. There was no pain, merely a chill tingle. She wriggled her fingers. They all seemed present and correct. She withdrew her hand and checked by sight-still all there.

"See, simple," Skellsgard said.

"I still don't like it."

"You don't have to. I'll go on ahead and show you how safe it is. There's a trick to this, so watch me closely. When I'm through you can pa.s.s me your hat."

Auger stood back. Skellsgard reached up and grasped the horizontal handrail above the censor firmly with both hands. With a gymnastic fluidity, she pulled herself up off her feet and swung her body towards the yellow surface. By the time she reached it she had gained sufficient momentum to push through in one movement. The surface puckered, then swallowed her with a snap. Auger's last glimpse was of the back of Skellsgard's head disappearing into the censor.

A moment later, a hand pushed through and snapped its fingers. Auger recognised the blunt fingernails. She removed her hat and offered it to the hand. Hand and hat vanished back through the censor.

Auger reached up and took hold of the handrail. She pulled herself from the ground, muscles screaming at the unaccustomed effort. She pulled her legs as high as they would go and swung herself into the yellow. It was almost certainly less elegant than Skellsgard's effort, but she supposed everyone had to begin somewhere.

The moment of transition, the pa.s.sage through the yellow, was like an electric shock without the pain. She felt every atom of her body flooded with a sharp, inquisitional light. She felt herself being scrutinised, rummaged through, turned this way and that like a cut gem. It lasted an eternity and an instant.

Then it was over, and she was lying in an undignified heap with the hem of her skirt somewhere around her hips and one shoe off her heel. Someone had thoughtfully arranged a padded mat on the other side of the censor.

"Here's your hat," Skellsgard said. "Welcome to Paris."

Auger picked herself up, straightened her clothes and placed the hat back on her head. The chamber in which they had arrived was much smaller than the last one, but it was crammed with a similarly bewildering a.s.sortment of machines and lockers. None of the contents looked quite as advanced, however: from what Auger could judge, almost everything here must have been sent through in tiny instalments and then rea.s.sembled (which naturally precluded anything really complicated) or-more likely-had been purloined from the outside world of E2 and then adapted to serve some new function. There was a lot of electrical equipment, ungainly humming things in grey or green metal cases, connected together with tangled rubberised cables; flickering monochrome screens, showing wave traces; black things like typewriters, but which clearly weren't. A generator chugged away in one corner.

"You feeling all right?" Skellsgard asked.

"More or less. Shouldn't I be?"

"There was a small risk that some of Niagara's machines might not have been flushed out before you came through. Didn't see any particular point in alarming you unnecessarily."

"I see," Auger said tersely.

"There's something else as well. Usually when we go through that thing, we don't feel anything. It only takes an instant and it's all over. But every now and then, something else happens. Maybe once in a hundred trips through the censor, it's different."

"Different in what way? Different as in painful?"

"No-not like that. It's just that sometimes it seems to take longer. Much longer-as if you're in that yellow limbo for a lifetime. You learn and feel things you can barely articulate. When you come out of it, you almost remember what it was like. It's like waking from a beautiful dream, clutching at threads as they fade away. You sense something of the minds that made this place. You feel them looking through you, vast and ancient and long dead, but still somehow aware, and curious as to what you make of their creation.

"Have you..."

"Once," Skellsgard said. "And that was enough. It's why I don't go through that thing any more often than I need to."

"Jesus," Auger said, shaking her head. "You might have told me this when I was on the other side. Now I have no choice but to go through it again."

"I just wanted you to know that if it does happen...which it probably won't...you shouldn't be afraid. Nothing bad will happen, and you'll come out of it in one piece. It's just a bit more than some of us can take."

"What were the minds like?" Auger asked, curiosity overcoming outrage, despite herself.

"Distant, huge and unchanging, like a range of mountains." Skellsgard smiled self-consciously, then shook her own head, as if trying to break a mental spell. "It never happened again. I got over it. We all have a job to do here. Talking of which, how do you like the set-up? This is effectively the nerve centre of E2 operations, the point from which we communicate with all the field agents."

Barton looked up from a folding table set with food and coffee. "Show her the Enigma."

"Her mission profile says she doesn't need to know about that," Skellsgard replied.

"Show her anyway."

Skellsgard shrugged and led Auger to a skeletal shelf unit containing about a dozen of the black typewriters. "You recognise these things?"

"Not really-they look like typewriters, but I'm sure they're something more sophisticated than that."

"They're Enigma machines," Skellsgard said. "Commercial enciphering equipment."

"Made locally?"

"Yes. The military use them, but anyone can buy an off the-shelf model for their own purposes. We use them to send secure messages to our field agents."

"Like Susan?"

"Exactly like Susan. Before she left here, we gave her one of these machines and instructions for converting a commercial wireless to intercept signals on our chosen frequency. Once she'd set up home, she used local tools and parts to modify the wireless. From our end, we encipher signals using an Enigma machine with the appropriate rotor settings for the given day of the month. Susan had a list of the settings so that she could set up her own Enigma accordingly. The enciphered messages came through the wireless in standard Morse code, but would have been completely unintelligible to anyone without an Enigma to decipher them back into plain text."

"Wait," Auger said, raising a hand. "I remember a little about these machines now. Didn't they play a role in the Second World War? Something involving submarine warfare?"

"Yes," Skellsgard said. "Enigma was cracked, eventually. It required several cunning breakthroughs in crypta.n.a.lysis methods and electromechanical computing. In fact, the task of cracking Enigma pretty much kick-started the entire computer revolution in the first place. But none of that happened here. There was no Second World War on E2."

"I figured as much from the map Caliskan sent me, but I didn't know what to make of it."

"Make of it what you like. Fact is, the E2 timeline diverges significantly from our history. On E2, the war fizzled out in nineteen forty. There was a brief front in the Ardennes, and then it was all over. The German advance stalled. A coup took out the leadership-Stauffenberg and Rommel were part of that- and within two years the n.a.z.i party had collapsed from within. People still talk about a Great War here, because there was never a second to rival it. No Second World War, no ma.s.sive endeavour to crack Enigma. Computing here is still stuck at the same level as in the nineteen thirties, which-to all intents and purposes-is pretty much the same as the eighteen thirties. And that's both good and bad. On the downside, it means we can't go out and steal computing equipment or any kind of sophisticated electronic hardware. There are no transistors, no integrated circuits or microprocessors. But we can be sure that no one on E2 is capable of deciphering our Enigma traffic."

"So you were using this thing to talk to Susan?"

"Yes," Skellsgard said. "But it was a strictly a one-way conversation. It's one thing to build a radio receiver. It's much more complicated to build a transmitter with the necessary range, and even more difficult to run it without drawing attention. Given time, she could have done it-we'd given her the instructions-but she was more interested in pursuing her own little investigation."

"The one that got her killed."

"I knew Susan. She wouldn't have allowed herself to get into something unless she felt the risks were worth it." "Meaning she was on to something? But according to Aveling..." Auger looked across to Barton, who had just raised his head, presumably on hearing Aveling's name. She lowered her voice. "But according to Aveling, the only reason Caliskan wants those papers back is in case the locals get their hands on them."

"Don't underestimate the danger of that," Skellsgard said. "It would only take one nudge in the right direction for them to realise they're inside an ALS. The illusion is good, but it isn't flawless."

"Still, you don't think that's the only reason, do you? It seems as if everyone here had a good opinion of Susan. If she said she was on to something-"

"Then maybe she was. But we won't know what it was until we get those papers back. And then hope

that there's enough of a clue in them."

"There's still one thing I don't get," Auger said, keeping her voice low. "Why me? If you know the territory as well, couldn't you have posed as this long-lost sister instead of dragging me halfway across the galaxy instead?"

"There's a catch," Skellsgard said.

"Another one? But of course there is. You know, I'm thinking I should start a collection."

"For some reason, Susan wanted you to be the sister. We know this from the last postcard she sent us."

Auger frowned. Up to this point, she had never had anything more than a distant professional

relationship with Susan White. Academic rivalry aside, she neither liked nor disliked the woman, but she didn't really know her at all. "I don't get it," she said.

"We didn't get it either."

"Couldn't one of you have just pretended to be the sister? A name's just a name, after all."

"There's more to it than that. She might have primed Blanchard with a physical description of you. She knew you by sight, didn't she?"

"Yes," Auger admitted, remembering the times they had b.u.mped into each other at conferences. "And we weren't so different in appearance, now that I think about it."

"We can't take the risk of sending in someone who doesn't fit Blanchard's expectations. If he gets suspicious-thinks he's being set up-then we may never see those papers again. That's why we need you."

"Then what Caliskan said was a lie. I was only ever the one candidate on his list."

"Guess he needed to appeal to your vanity," Skellsgard said.

"Guess it worked, too."

TWELVE.

Floyd continued his tour of the building in rue des Peupliers, knocking on doors and sometimes getting an answer. He worked methodically and patiently, turning on the charm when it was required. By the end of his enquiries, it was clear that at least two other tenants had seen the girl in the building, hanging around on the stairs. They couldn't be specific about dates, but the sightings had all occurred within the last three or four weeks: consistent with there being a link to the White case. Once observed, the girl was not usually seen again by the same witness. Another tenant might have seen an odd child in the street outside, but he was insistent that this child had been a boy rather than a girl. Floyd and Custine had seen a strange girl leaving the Blanchard building the evening before, and Floyd had noticed what he thought was a different girl watching White's window from outside earlier that day. Floyd still hadn't spoken to the witness on the second floor, the one who had mentioned a child to Custine the night before.

Floyd had no idea what to make of it all. Strange little children hadn't figured prominently in any of his previous investigations. Perhaps he was latching on to any anomaly in the hope that it might break open the case. Maybe if he visited any similar apartment building in the city and asked a similar set of questions he'd get a similar set of responses.

He was done by four. He walked back up to Susan White's room and knocked on the door. His shirt was sticky around the collar. All that trudging up and down the stairs was making him sweat.

"You get anywhere, chief?" he asked Custine when he opened the door.

Custine let Floyd inside and closed the door. "No. There've been no further transmissions. I removed the back of the wireless again, thinking that one of my connections might have come loose, but all was well. The station is simply not on the air."

"Maybe they've gone off the air for good."

"Perhaps," Custine said. "All the same, I shall try again tomorrow. Perhaps the transmissions only take place at a certain time of day."

"You can't spend the rest of your life up here."

"One more day, that's all."

Floyd knelt down next to Custine. "Show me what you got before."

"It's incomplete."

"I'd like to see it anyway." Custine removed a sheet of paper from the top of the wireless set on which he'd marked a sequence of dots and dashes in neat pencil. "You can see the pieces I missed," he said. "Of course, there's no guarantee that tomorrow's transmission will be the same as today's. But at least I'll be ready for it tomorrow. I should be able to make an accurate transcription."

"If you haven't got anything by the middle of the day, we close this line of enquiry."

"There is something going on here, whether you like it or not."

"Maybe there is, but we can't waste Blanchard's money just sitting around waiting for a transmission

that may never return. There are other leads that need to be followed up."

"Generated by the material Greta examined?"

"That, and something else." Quickly he told Custine about the paperwork in the tin and what Greta made