The loudspeaker addressed the crowd again. I tried to follow the commentator's words, but my brain failed to translate the sounds. The ugly and violent impact of this simulated crash, the rupture of metal and safety glass, and the deliberate destruction of expensively engineered artefacts, had left me lightheaded.

Helen Remington held my arm. She smiled at me, nodding encouragingly as if urging a child across some mental hurdle. 'We can have a look at it again on the Ampex. They're showing it in slow-motion.'

The crowd was moving towards the trestle tables, voices lifting again in relieved chatter. I turned back, waiting for Vaughan to join us. He was standing among the empty seats, eyes still fixed on the wrecked car. Below his waistband a pool of semen darkened the crotch of his trousers.

Ignoring Helen Remington, who moved away from us with a faint smile, I stared at Vaughan, uncertain what to say to him. Faced with this junction of the crashed car, the dismembered mannequins and Vaughan's exposed sexuality, I found myself moving through a terrain whose contours led inside my skull towards an ambiguous realm. I stood behind Vaughan, staring at his muscular back, hard shoulders swinging under his black jacket.

Beside the Ampex machine the visitors were watching the motorcycle as it crashed once again into the saloon car. Sections of the collision were replayed in slow motion. In a dream-like calm, the front wheel of the motorcycle struck the fender of the car. As the rim collapsed, the tyre sprung inwards upon itself to form a figure of eight. The tail of the machine rose into the air. The mannequin, Elvis, lifted himself from his seat, his ungainly body at last blessed by the grace of the slow-motion camera. Like the most brilliant of all stunt men, he stood on his pedals, legs and arms fully stretched. His head was raised with its chin forwards in a pose of almost aristocratic disdain. The rear wheel of the motorcycle lifted into the air behind him, and seemed about to strike him in the small of the back, but with great finesse the rider detached his feet from the pedals and inclined his floating body in a horizontal posture. His hands were still attached to the handlebars, now moving away from him as the cycle somersaulted. The metering coils severed one wrist, and he launched himself into a horizontal dive, head raised so that his face became a prow, bearing its painted wound areas towards the oncoming windshield. His chest struck the bonnet of the car, grazing its polished cellulose like a surfboard.

Already, as the vehicle moved back under the impact of the first collision, the four occupants of the car were themselves moving towards the second collision. Their smooth faces pressed on into the advancing windshield as if eager to see the chest glider soaring up the bonnet of the car. Both the driver and his woman passenger rolled forwards to meet the windshield, touching it with the crowns of their lowered heads at the same moment as the motorcyclist's profile struck the glass. A fountain of spraying crystal erupted around them, through which, as if in celebration, their figures were taking up ever more eccentric positions. The motorcyclist continued on his horizontal path through the emblazoned windshield, his face torn away by the centrally mounted driving mirror. His left arm detached itself at the elbow as it struck the windshield pillar, and was swept up through the fountain of glass to join the debris chasing the inverted body of the motorcycle three feet above his spine. His right arm moved through the fractured windshield, losing first its hand on the guillotine of the near-side windshield wiper, and then its forearm against the face of the front-seat woman passenger, taking with it her right cheekbone. The motorcyclist's body slewed gracefully to one side in an elegant slalom, his hips striking the right-hand windshield pillar, buckling it at the central welding point. His legs rotated around the car, shin-bones striking the central door pillar.

Above him, the inverted motorcycle fell on to the car's roof. Its handlebars passed through the empty windshield and decapitated the front-seat passenger. The front wheel and chromium fork assembly plunged through the roof, the whiplashing drive chain severing the cyclist's head as he swept past. The pieces of his disintegrating body rebounded off the rear wheel-housing of the car and passed over the ground in the haze of broken safety glass which fell like ice from the car, as if it had been defrosted after a long embalming. Meanwhile, the driver of the car had rebounded off the collapsing steering wheel and was sliding beneath the column into the lower compartment of the car. His decapitated wife, hands raised prettily in front of her neck, rolled against the instrument panel. Her detached head bounced off the vinyl seat covering and passed between the torsoes of the children in the rear seat. Brigitte, the smaller of the two children, lifted her face to the roof of the car and raised her hands in a polite gesture of alarm as her mother's head struck the rear window and cannonaded around the car before exiting through the left-hand door.

The car slowly came to rest, continuing to heave itself laboriously off the ground. The four passengers subsided into the glass-embroidered cabin space. Their signalling limbs, busy with an encyclopedia of unheeded semaphores, settled again into a crudely human posture. Around them, the fountain of frosted glass moved away for the last time.

The audience of thirty or so visitors stared at the screen, waiting for something to happen. As we watched, our own ghostly images stood silently in the background, hands and faces unmoving while this slow-motion collision was re-enacted. The dream-like reversal of roles made us seem less real than the mannequins in the car. I looked down at the silk-suited wife of a Ministry official standing beside me. Her eyes watched the film with a rapt gaze, as if she were seeing herself and her daughters dismembered in the crash.

The visitors wandered away to the tea tent. I followed Vaughan towards the crashed car. He stepped between the chairs, spitting his chewing-gum on to the grass. I knew that he had been even more affected by the test crash and the slow-motion film than myself. Helen Remington watched us, sitting alone among the chairs. Vaughan stared down at the shattered car, almost about to embrace it. His hands roved along the torn bonnet and roof, the muscles of his face opening and shutting like manacles. He bent down and peered into the cabin, scanning each of the mannequins. I waited for him to say something to them, my eyes moving from the dented curvatures of the bonnet and fenders to the cleft of Vaughan's buttocks. The destruction of this motor-car and its occupants seemed, in turn, to sanction the sexual penetration of Vaughan's body; both were conceptualized acts abstracted from all feeling, carrying any ideas or emotions with which we cared to freight them.

Vaughan scraped the flaking fibreglass from the driver's face. He wrenched the door open and edged his thigh on to the seat, one hand holding the distorted steering wheel.

'I've always wanted to drive a crashed car.'

I took the remark to be a joke, but Vaughan appeared to mean it seriously. Already he was calmer, as if this act of violence had drained some of the tensions from his body, or pre-empted whatever violent behaviour he had suppressed for so long.

'All right,' Vaughan announced, dusting the fibreglass from his hands. 'We'll leave now – I'll give you a lift.' When I hesitated he said, 'Believe me, Ballard, one car-crash looks like another.'

Was he aware that I was duplicating in my mind a series of sexual postures between Vaughan and myself, Helen Remington and Gabrielle which would re-enact the death-ordeals of the mannequins and the fibreglass motorcyclist? In the urinal beside the car-park Vaughan deliberately exposed his half-erect penis as he stood well back from the stall, flicking out the last drops of urine on to the tiled floor.

Once away from the Laboratory he recovered all his aggressiveness, as if bis appetite was quickened by the passing cars. He rolled the heavy car along the access road to the motorway, holding the battered bumpers a few feet behind any smaller vehicle until it moved out of his way.

I tapped the instrument panel. 'This car – a ten-year-old Continental. I take it that you see Kennedy's assassination as a special kind of car-crash?'

'The case could be made.'

'But why Elizabeth Taylor? Driving around in this car, aren't you putting her in some danger?'

'Who from?'

'Seagrave – the man's half out of his mind.'

I watched him drive along the last stretches of the motorway, making no effort to slacken his speed despite the warning signs.

'Vaughan – has she ever been in a car-crash?'

'Not a major crash – it means that everything lies in the future for her. With a little forethought she could die in a unique vehicle collision, one that would transform all our dreams and fantasies. The man who dies in that crash with her…'

'Does Seagrave appreciate this?'

'In his own way.'

We approached a major trunk roundabout. For almost the first time since we had left the Road Research Laboratory Vaughan applied the brakes. The heavy car swayed and went into a long right-hand slide which carried it across the path of a taxi already making its way around the island. Flooring the accelerator, Vaughan swerved in front of it, tyres screaming over the blaring horn of the taxi. He shouted through his open window at the driver and pressed on towards the narrow canyon of the northbound slip road.

As we settled down Vaughan reached behind him and lifted a briefcase off the back seat.

'I've been testing people for the programme with these questionnaires. Tell me if I've left anything out.'