A white Transit van bursts into view round the corner from Green Street, its engine racing, its rear door slamming shut. The child and her abductor are inside. That is understood by all, or intuited, for only the woman has seen them scramble aboard. A second man is driving the van. That is also understood, though no-one catches so much as a glimpse of him amidst what follows.

The man in the fisherman's waistcoat has taken a few ineffectual strides after the woman, but has now turned back. The boy is standing stock-still between Adam and Eve, paralysed by an inability to decide what to do or who to follow.

No such indecision grips his sister, though. She is running, ponytail flying, towards the gate onto the main road. What is in her mind is uncertain. From where she was standing, she will have seen the van pull away. She knows her sister is being stolen from her. She is not equipped to prevent the theft, yet she seems determined to try. She flicks up the latch on the gate and darts through.

The van turns right onto the main road. A northbound car, slowing for the bend, brakes sharply to avoid a collision and blares its horn. The driver of the van pays this no heed as he accelerates through a skid, narrowly avoiding the boundary wall of the pub car park.

The girl does not pause at the edge of the road. She runs forward, into the path of the van. She turns towards it and raises her hands, as if commanding it to stop. There is probably just enough time for the driver to respond. But he does not. The van surges on. The girl holds her ground. In a breathless fraction of a second, the gap between them closes.

There is a loud thump as hard steel hits soft flesh. There is a blurred parabola through the air of the girl's frail, flying body. There is the speeding white flank of the van and the slower-moving dark green roofline of the following car. Neither vehicle stops. The car driver proceeds as if he has seen nothing. And maybe he has somehow failed to register what has occurred. He does not have to swerve to avoid the crumpled shape at the side of the road. He simply carries on.

The van and the car vanish round the next bend in the road. All movement ceases. All sound dies.

It is only for a second. Soon everyone will be running. The boy will be crying. The woman will be screaming. The man who was drinking outside the Red Lion will be hopping over the wall of the car park, his eyes fixed on the place at the foot of the opposite verge where the girl lies, her blue and white dress stained bright red, the tarmac beneath her darkening as a pool of blood spreads across the road. And her eyes will seem to meet his. And to hold them in her sightless gaze.

But that is not yet. That is not this second. That is the future, a future forged in the stillness and the silence of this frozen moment.

It begins at Avebury. But it does not end there.

It had been a fickle winter in Prague. Yet another mild spell had been cut short by a plunge back into snow and ice. When David Umber had agreed to stand in as a Jolly Brolly tour guide for the following Friday, he had not reckoned on wind chill of well below zero, slippery pavements and slush-filled gutters. But those were the conditions. And Jolly Brolly never cancelled.

Umber's exit from the apartment block on Sokolovska that morning was accordingly far from eager. A lean, melancholy man in his late forties, his dark hair shot with grey, his eyes downcast, his brow furrowed with unconsoling thoughts, he turned up the collar of his coat and headed for the tram stop, glancing along the street to see if he needed to hurry.

He did not. There was no tram in sight, giving him a chance to examine the letter he had found in his mailbox on the way out. Deducing from the typeface visible through the envelope-window that it was in fact a bank statement, he thrust it back into his pocket unopened and pressed on to the tram stop.

God, it was cold. Not for the first time when such weather prevailed, he silently asked himself, 'What am I doing here?'

The answer, he knew, was best not dwelt upon. He had stayed on after the end of his teaching contract last summer because of Milena. But Milena had gone. And so had the temporary post he had found for the autumn term. He had a small circle of friends and acquaintances in Prague, happily including Ivana, Jolly Brolly coordinator and entrepreneuse manquee. But he also had plenty of evidence to strengthen his sense of drift and purposelessness.

He stood at the stop, shifting from foot to foot in an effort to keep warm, or at least to avoid getting any colder. The heating in his apartment block was in dire need of an overhaul. That could in fact be said of pretty much everything in the block. He had moved there as a stopgap measure when his much more salubrious and ironically cheaper flat near Grand Priory Square had vanished under the waters of the Vltava during the cataclysmic flood of August 2002. He had been in England at the time, but virtually all his possessions had been in the flat. The flood had claimed those tangible reminders of his past, leaving a void in his sense of himself that the sixteen months since had failed to fill.

The red and white nose of a tram appeared through the murk. Those waiting at the stop shuffled forward, some of them taking last drags on their cigarettes before flicking the butts into the slush. Umber squinted towards the tram, struggling to read its route number. It was a 24. Well, that was something. If it had been an 8, he would have had to stand there for another bone-chilling few minutes.

The number 24 pulled up and the passengers piled aboard, Umber hopping onto the second car, where there were more vacant seats. He slumped down in one and closed his eyes for a restful few moments as the tram started away. As a result, he did not notice the short, barrel-chested man muffled up in parka, gloves, scarf and woolly-hat who jumped on just as the doors were closing. He had no cause to be on his guard, after all. A Prague tram at the back end of winter was hardly where he would have expected the past to creep up on him. He was not thinking about any of that.

But then he did not need to. David Umber's past was of an order that did not allow for genuine forgetting. It was not necessary to apply his mind to it consciously. It was simply there, always, pulling him back, dragging him down. It would never leave him. All he could do was refine his tactics of evasion. And this, he knew but did not care to admit, was why he had stayed on in Prague. It was a refuge, a hiding-place. It was far from anywhere tainted by all that he did not wish to recall. But it was not, he was to discover before the day was out, far enough.

The tram trundled on through the streets, picking up more passengers than it shed, so that by the time it reached Wenceslas Square it was crammed. Umber got off with a mob of others and headed for the Wenceslas Monument in front of the National Museum. That was the appointed meeting-place for those hapless tourists who had decided to spend a thousand koruna on a six-hour walking tour of the city's principal attractions, with lunch thrown in, in the care of an old Prague hand replete with local lore. Golly Brolly never knowingly undersold itself.)

About a dozen tourists were waiting by the statue of Bohemia's patron saint. The cold weather had taken its toll on numbers, for which Umber was grateful. He would not have to shout to make himself heard by such a small group. They were the usual mix of ages and nationalities, clutching their polyglot of guidebooks. Ivana was in the process of unburdening them of their cash. She acknowledged Umber's arrival with a relieved smile.