Helen gathered up her equipment and they walked side by side through the intersecting corridors between one square and the next. Though the estate was low-rise, each court only five storeys high, the effect of each quadrangle was horribly claustrophobic. The walkways and staircases were a thief's dream, rife with blind 'corners and ill-lit tunnels. The rubbish-dumping facilities - chutes from the upper floors down which bags of refuse could be pitched - had long since been sealed up, thanks to their efficiency as fire-traps. Now plastic bags of refuse were piled high in the corridors, many torn open by roaming dogs, their contents strewn across the ground. The smell, even in the cold weather, was unpleasant. In high summer it must have been overpowering.

'I'm over the other side,' Anne-Marie said, pointing across the quadrangle. 'The one with the yellow door.' She then pointed along the opposite side of the court. 'Five or six maisonettes from the far end,' she said. 'There's two of them been emptied out. Few weeks now. One of the family's moved into Ruskin Court; the other did a bunk in the middle of the night.'

With that, she turned her back on Helen and wheeled Kerry, who had taken to trailing spittle from the side of his pushchair, around the side of the square.

'Thank you,' Helen called after her. Anne-Marie glanced over her shoulder briefly, but did not reply. Appetite whetted, Helen made her way along the row of ground floor maisonettes, many of which, though inhabited, showed little sign of being so. Their curtains were closely drawn; there were no milk-bottles on the doorsteps, nor children's toys left where they had been played with. Nothing, in fact, of life here. There was more graffiti however, sprayed, shockingly, on the doors of occupied houses. She granted the scrawlings only a casual perusal, in part because she feared one of the doors opening as she examined a choice obscenity sprayed upon it, but more because she was eager to see what revelations the empty flats ahead might offer.

The malign scent of urine, both fresh and stale, welcomed her at the threshold of number 14, and beneath that the smell of burnt paint and plastic. She hesitated for fully ten seconds, wondering if stepping into the maisonette was a wise move. The territory of the estate behind her was indisputably foreign, sealed off m its own misery, but the rooms in front of her were more intimidating still: a dark maze which her eyes could barely penetrate. But when her courage faltered she thought of Trevor, and how badly she wanted to silence his condescension. So thinking, she advanced into the place, deliberately kicking a piece of charred timber aside as she did so, in the hope that she would alert any tenant into showing himself.

There was no sound of occupancy however. Gaining confidence, she began to explore the front room of the maisonette which had been - to judge by the remains of a disemboweled sofa in one corner and the sodden carpet underfoot - a living-room. The pale-green walls were, as Anne-Marie had promised, extensively defaced, both by minor scribblers - content to work in pen, or even more crudely in sofa charcoal - and by those with aspirations to public works, who had sprayed the walls in half a dozen colours.

Some of the comments were of interest, though many she bad already seen on the walls outside. Familiar names and couplings repeated themselves. Though she bad never set eyes on these individuals she knew how badly Fabian J. (A.OK!) wanted to deflower Michelle; and that Michelle, in her turn, had the hots for somebody called Mr Sheen. Here, as elsewhere, a man called White Rat boasted of his endowment, and the return of the Syllabub Brothers was promised in red paint. One or two of the pictures accompanying, or at least adjacent to, these phrases were of particular interest. An almost emblematic simplicity informed them. Beside the word Christos was a stick man with his hair radiating from his head like spines, and other heads impaled on each spine. Close by was an image of intercourse so brutally reduced that at first Helen took it to illustrate a knife plunging into a sightless eye. But fascinating as the images were, the room was too gloomy for her film and she had neglected to bring a flash. If she wanted a reliable record of these discoveries she would have to come again, and for now be content with a simple exploration of the premises.

The maisonette wasn't that large, but the windows had been boarded up throughout, and as she moved further from the front door the dubious light petered out altogether. The smell of urine, which had been strong at the door, intensified too, until by the time she reached the back of the living-room and stepped along a short corridor into another room beyond, it was cloying as incense. This room, being furthest from the front door, was also the darkest, and she bad to wait a few moments in the cluttered gloom to allow her eyes to become useful. This, she guessed, had been the bedroom. What little furniture the residents had left behind them had been smashed to smithereens. Only the mattress had been left relatively untouched, dumped in the corner of the room amongst a wretched litter of blankets, newspapers, and pieces of crockery.

Outside, the sun found its way between the clouds, and two or three shafts of sunlight slipped between the boards nailed across the bedroom window and pierced the room like annunciations, scoring the opposite wall with bright lines. Here, the graffitists had been busy once more: the usual clamour of love-letters and threats. She scanned the wall quickly, and as she did so her eye was led by the beams of light across the room to the wall which contained the door she had stepped through.

Here, the artists had also been at work, but had produced an image the like of which she had not seen anywhere else. Using the door, which was centrally placed in the wall, as a mouth, the artists had sprayed a single, vast head on to the stripped plaster. The painting was more adroit than most she had seen, rife with detail that lent the image an unsettling veracity. The cheekbones jutting through skin the colour of buttermilk; the teeth - sharpened to irregular points - all converging on the door. The sitter's eyes were, owing to the room's low ceiling, set mere inches above the upper lip, but this physical adjustment only lent force to the image, giving the impression that he had thrown his head back. Knotted strands of his hair snaked from his scalp across the ceiling.

Was it a portrait? There was something naggingly specific in the details of the brows and the lines around the wide mouth; in the careful picturing of those vicious teeth. A nightmare certainly: a facsimile, perhaps, of something from a heroin fugue. Whatever its origins, it was potent. Even the illusion of door-as-mouth worked. The short passageway between living-room and bedroom offered a passable throat, with a tattered lamp in lieu of tonsils. Beyond the gullet, the day burned white in the nightmare's belly. The whole effect brought to mind a ghost train painting. The same heroic deformity, the same unashamed intention to scare. And it worked; she stood in the bedroom almost stupified by the picture, its red-rimmed eyes fixing her mercilessly. Tomorrow, she determined, she would come here again, this time with high-speed film and a flash to illuminate the masterwork.

As she prepared to leave the sun went in, and the bands of light faded. She glanced over her shoulder at the boarded windows, and saw for the first time that one four-word slogan had been sprayed on the wall beneath them.

'Sweets to the sweet' it read. She was familiar with the quote, but not with its source. Was it a profession of love? If so, it was an odd location for such an avowal. Despite the mattress in the corner, and the relative privacy of this room, she could not imagine the intended reader of such words ever stepping in here to receive her bouquet. No adolescent lovers, however heated, would lie down here to play at mothers and fathers; not under the gaze of the terror on the wall. She crossed to examine the writing. The paint looked to be the same shade of pink as had been used to colour the gums of the screaming man; perhaps the same hand?