He saw a hole in the tarmac in front of him (and was vaguely aware of people on the pavement, waiting for buses, as their faces flashed by on the far side of the truck's flat deck). The long hole in the road surface ahead of him wasn't too large; he could avoid it and the long dark plume of disintegrating tarmac strewn out on its far side; he swerved the bike neatly.

At first it looked as though the lorry with the beer barrels would miss the hole, too, but it swerved suddenly towards the hole and bike - as though avoiding somebody stepping out into the road from the bus-stop - and its wheels went thumping, crashing into the ragged trench in the roadway with a huge hollow-sounding noise, and from the truck's lightly laden, suddenly bouncing rear, something flew into the air...

Graham walked up the street, through the hard sunlight of the late afternoon, over Penton Street and into an area where most of the buildings had been demolished. Around him were some echoes of buildings; rows and corridors of corrugated iron, new and zinc-bright in the sunlight, standing on end around empty, dusty sites where weeds grew; in the distance were old buildings, tall crumbling places, leaning and twisted, worn old slates with many missing, roofs bowed under the ancient weight, old windows, glaucomaed with age, eaten timbers making up ramshackle additions to the top storeys. New kerbs, un-made-up pavements, dust and sand. He caught glimpses of the empty sites through spaces in the corrugated iron. Most were flat, filled with swirled patterns of rubbish and growing weeds. Some were being worked on; he saw the naked bricks and ragged lengths of concrete-bottomed trenches which would become foundations; lengths of string marked lines and levels for bricks.

He walked through this summit of iron and dust, seeing it but numb to it, through the slightly humid air and the sounds of the traffic and sirens, through the smells of cement dust and rotting rubbish, down to Liverpool Road and over towards Upper Street.

He could only think of what had just happened to him as something he had watched, not actually taken part in. He could not appreciate it directly, he could not cope with it in any personal way, on a level which related to what he regarded as his real self. It was something too important to be assimilated quickly; it was as though some vast besieging army had finally smashed the main gate into a great city, and swept in to overwhelm its ruined defences but could do so only through that one point, so that, while the forces spread throughout the streets and houses and the city's fall was assured, already underway, for a long time in many places within it there was nothing immediately wrong or affected, and life could go on almost as normal.

When he got down to Upper Street there was a traffic jam, and the flashing blue light of an ambulance waiting somewhere at the bus-stops; people were looking in that direction, trying to see over the tops of the other people's heads, edging closer, trying to find out what happened. He could not go near, did not want to see other people.

He crossed the lanes of stationary traffic, waited for a break in the still moving south-bound streams, crossed to the far side, walked past another huge building site where tall cranes stuck into the sky and dust moved in the wind, then went down through smaller streets, ignoring people, clutching the black portfolio to : him, heading towards some trees he could see.

Richard Slater lay in bed with his elder sister, the woman Graham knew as Mrs Sara ffitch, but whose real name was Mrs Sarah Simpson-Wallace (nee Slater).

The shared, mingled sweat dried on their naked bodies. Sarah took another Kleenex from the box under the bed, dabbed at herself, then put the soggy tissues in the small split-cane bin at the foot of the bed. She got up, stretching her arms and shaking her black, tangled hair.

Slater watched her. He had bruised her again. Dark blue marks were forming on the tops of her arms, and under her buttocks, at the top and rear of her thighs. He had bitten her, too, on the white scar (where she didn't feel it so much). She had whimpered at the time; cried out, but - perhaps because she was relieved she had received no physical retaliation from Graham - she did not seem to be in a mood to complain today. Still, Slater felt guilty anyway. He was too rough, and despised himself - and maybe even her - for it. He had never been like that with anybody else, never even felt like being that way. With her, he couldn't help it. He wanted to be like that, he wanted to grip her, squeeze her, to impale and imprison her, to shake and pummel her; mark her. It was that or it was nothing; cold, without feeling, almost masturbatory.

Why? he asked himself for the thousandth time. Why do I do that to her? Why do I need to? He knew he wasn't like that really. It went against everything he believed in. So why?

Sarah took a plain, blue silk dressing gown from the bottom of the bed and tied it around her. She still wore the pink training shoes she had put on after her bath.

Slater sighed. He said, "None of which alters the fact that you shouldn't have done it, not without me here."

Sarah shrugged, without turning round. "I'm going to have some orange juice," she said. "Want some?"

"Sarah."

"What?" She turned to look at him. Slater looked at her accusingly. She grinned back at him. "I handled it," she said. "Nothing went wrong, did it?"

"He's bigger than you are. He might have got violent. He is a man, after all, dear. We chaps are all the same, didn't you know?" He could not resist smiling as he said it.

"Luckily, you aren't all the same at all," Sarah said, and went through the doorway, across the hall to the sitting-room and kitchen. "Not at all," she said from the other room as she walked. "Not even slightly."

Slater lay on the bed, shivering once as his flesh dried. He got up and took a piece of paper from the small dressing table by the side of the bed. It was an old Labour election leaflet, blank on one side. He took a pen from the inside pocket of his biker leathers - strewn on the floor with her dungarees and T-shirt - then sat up in bed and started to write, quickly and in a small, scratchy, precise hand.

He wrote:

Dear Graham,

I know what Sarah has told you. It was not the whole truth. I'm afraid. The fact is that I am Stock (and so, once, was Sarah, as I'll explain). There is no Bob Stock, there's only me.

Sarah is my sister and we've had (horror of horrors!) an incestuous relationship for the past six years or so (blame single-sex public schools, I say). Sarah is married and her husband was having her followed. I couldn't risk being seen with her, so I invented Stock; I keep the bike in a car park at the back of the Air Gallery; I know somebody who works there and they keep the leathers and crash helmet. I dress there and visit Sarah using the bike, looking terribly butch and incognito.

So far so good, you might think, but we needed more; it wasn't all that important that Sarah was known to be committing adultery, but it was important, at least until very recently, that it wasn't known who with. Quite apart from the fact that what we're doing is reasonably illegal, it would have done terrible things to our parents. Dear dad, you see, was Conservative MP for Salop West. Even you might have heard of him; very strong line on family life, morality and that son of thing; supported the Festival of Light, the National Viewers and Listeners Association (Mary White-house's mob), and SPUNK, or whatever they call it; the Society for the Prevention of Unborn Conservatives (sick!). Pro-hanging, of course.

The old bugger having made his reputation peddling this sort of reactionary moralist nonsense, the revelation that his two children were humping each other would have finished him; that applied at the start of all this, but became even more important when Mag the Hag announced the election. Anyway, going back to where you came in, I think you'll appreciate that the situation was such that we needed another safeguard to stop me being identified. We needed somebody else, to draw the heat, to distract the chap we knew was trailing Sarah. We chose you. All right; I chose you.