He sat up with a start and said, in Arabic: 'That's what you are Ava, a Dust-Counter, 'Addaad al-Turaab.'

He said it under his breath, but Ava heard him anyway. He could have sworn that she was actually startled: her 'eye', a laser-guided surveillance camera, swivelled on him while the screen misted over with standby graphics. Then Ava began to spit out translations of the Arabic phrase, going through the world's languages in declining order of population: Mandarin, Spanish, English, Hindi, Arabic, Bengali… It was funny at first, but when it got to the dialects of the Upper Amazon Antar couldn't bear it any longer. 'Stop showing off,' he shouted. 'You don't have to show me you know everything there is to know. Iskuti; shut up.'

But it was Ava who silenced him instead, serenely spitting the phrases back at him. Antar listened awestruck as 'shut up' took on the foliage of the Upper Amazon.

Chapter 2

ANTAR WAS WAITING to sign off when the card and chain showed up on Ava's screen. His eyes kept straying to the timeline; he'd been hoping to get off a few minutes early. His neighbour, a young woman who had moved in next door a few months earlier, had invited herself over that evening. She was going to bring dinner. Antar wanted some time to himself before she came: he'd been planning to get a shower and go for his usual evening walk to Penn Station. There was still half an hour to go before he got off, at six.

Restive as he was, Antar probably wouldn't have given the card a second glance; left to himself, he'd have disspatched it with a keystroke, sent it tumbling into the unbounded darkness of Ava's heart. It was only because Ava went into one of her trances of unrecognition over the metal chain that he took a closer look.

The chain was made up of very small interlocking metal spheres. It was scuffed and rusted with all the nickel-plating gone, but Antar knew what it was the moment he saw it. He'd worn one himself, for years, while he was working at LifeWatch.

LifeWatch was a small but respected non-profit organization that served as a global public health consultancy and epidemiological data bank. Antar had worked there much of his life, as a programmer and systems analyst. In a sense he worked there still except that LifeWatch had long since been absorbed, along with many other such independent agencies, into the mammoth public health wing of the newly formed International Water Council, Like most of hi,s colleagues, Antar had been assigned to an inconsequential 'At Home' job to see him through to retirement. He was still technically on the Council's payrolls, but he had never set foot in its New York offices. He had not had reason to: they communicated with him through Ava whenever they wanted, which wasn't often.

Antar could remember a time when those little chains had been standard issue at LifeWatch, along with bar-coded identity cards. Some people preferred to wear their cards on clips; he'd always liked the chains himself. He liked the feel of the metal balls, running through his fingernails; they were like miniature worry-beads.

He lingered over the chain for a moment. They hadn't been around for years now and he couldn't quite recall when they were first introduced: probably some time in the 1980s. He had been at LifeWatch for well over ten years by that time. He had joined immediately after graduating from Patrice Lumumba University in Moscow: this was in the days when the Russians were still handing out scholarships to students from poor countries; when Moscow was the best place in the world to study linear programming. Life Watch had advertised internationally for a programmer and analyst, to bring their accounts online. It was a number-crunching job, not what he had been trained for. But, on the other hand, it was safe, secure, settled, and it offered an American salary and a guaranteed visa. He'd responded immediately, without really expecting to get the job: he knew the competition would be fierce. As it turned out, he was third on the shortlist but the two people who were ahead of him got other offers.

Antar rubbed his fingertips, overcome by a tactile nostalgia, recalling the feel of those chains and those laminated plastic ID cards. The chains came in two sizes, he rememmbered: you could wear them around your neck or thread them through a buttonhole. He'd always preferred the shorter chains.

He took his time, keying in answers to Ava's questions. In the meanwhile Ava was toying with the card, flipping it over, blowing up segments in random order.

Suddenly a symbol flashed across the monitor, shooting off at an angle, rotating and diminishing as it went. It caught Antar's eye just before it spun off the edge of the screen. He lunged at the keyboard, and tracked slowly back. When he had the symbol centred he froze the frame.

It was years since he'd seen the once-familiar logo of LifeWatch, a neatly stylized image of two intertwined laurel wreaths. And here it was now, in front of him, plucked out of the bottom of a lost ID card. Antar turned the card over, on Ava's screen, intrigued at the sight of the symbol, so well known and so long forgotten. He brought the card back on screen, life size, and blew it up, slowly. There couldn't be any doubt about it: it was a LifeWatch ID.

He guessed the card was from the mid-eighties or early nineties or thereabouts – a time when he had spent so many hours with spreadsheets that he'd got to know every name that ever appeared on Life Watch's payroll. Looking at that grubby old card suspended in front of him he began to wonder whom it had belonged to. He was sure he'd know the name – that at the very least. He might even recognize the face in the picture.

Without thinking, he tapped in a sequence of commands. Ava's screen went momentarily blank as she began reconstructing the card, restoring the original. Almost immediately Antar regretted the command. The process could take a while, and sign-off time was just twenty-five minutes away now. He gave his chair a kick, annoyed with himself. As the chair spun around, he noticed that a word had appcared on the screen, under a line that said 'Point of Origin'. Jamming his foot on the floor, he brought the chair to a halt.

He didn't usually bother to check where the inventories originated: they came through in such quantities it didn't seem to matter much. But he was curious now, especially when ' Lhasa ' appeared on his screen. He tried to think back to the eighties and nineties and whether Life Watch had had an office there at the time. Then he noticed that the word ' Lhasa ' was prefixed by a symbol which indicated that the item had merely joined the information flow there. It had been found somewhere else.

He looked over his shoulder and discovered that the pale outline of an enormous white triangle had begun to materrialize in his living room, a few feet away. Ava had started to create a holographic projection of the reconstructed card: the cloudy triangle represented the top left-hand corner, hugely magnified. He began to drum his fingers on the arms of his chair, wondering whether he had the energy or the inclination to ask Ava where the card had been found. It was always hard to tell when something came through Lhasa.

Lhasa was the International Water Council's continental command centre for Asia. The Council's officers called it the de facto capital of Asia because it had the unique distinction of being the only command centre in the world that was in charge of not one but several major Hydraulic Regions: the Ganges-Brahmaputra, the Mekong, the trans-Yangtze, the Hwang-Ho. The Council's information streams for the eastern half of the continent were all routed through Lhasa. This meant that the card could have entered the system anywhere between Karachi and Vladivostok.

He looked over his shoulder again. Ava was taking longer than he'd thought: she was just getting started on the photograph, at the top right-hand corner of the card. He glanced at the timeline. He really didn't have much time if he was going to walk down to Penn Station before his neighbour, Tara, came over.