I'd done what I could at the Esso station, telling the man to shut off at twenty-five litres. That amount would get me to Hanover if necessary and left the N.S.U. lighter.

Workable findings: assume the best figures — both men were heavy and their tank was full and it would cost them 10 k.p.h. in maximum speed. Add 1 k.p.h. In one hour there would be a kilometre's distance between us and with that kind of margin I could peel off at whatever loop-road I liked: Braunschweig Hildesheim, Hanover itself. And they wouldn't see me go. Assume, the worst figures — both men were average weight and they had a quarter tankful and they had the edge on me in terms of maximum speed. The extra weight of one man would bring down the speed fractionally but not the full 10, k.p.h.

Conclusion: the Mercedes had to be faster than the N.S.U. by 1 k.p.h. if they were going to stay with me and send me into the trees. I believed on the figures alone that it was 1 k.p.h. faster and that they could do that.

There was only the one area in which I could hope to work, hope to avoid a mathematical certainty. The N.S.U. had a rotary engine and was lighter by 350 kilos and that gave me the edge on them in acceleration. I was already establishing a lead: that was why they'd just put their headlights on. They were worried. Their idea would be to stay with me almost bumper-to-bumper with their lights out so that I couldn't see enough in the mirror to judge how close they were, couldn't see which side they were creeping up on to shape for the final nudge.

The N.S.U.'s superior acceleration and the Mercedes' higher top speed would vary the distance between us as we went north. It would be like a Chriscraft towing a water-skier on a long piece of elastic: the N.S.U. would draw ahead and then the tension would be taken up and the Mercedes would close the gap until it hit.

The only outside factor that could come into play was the presence of other cars making north. But we were both going to take it right up to the ceiling and there wasn't likely to be anyone driving in the 180–190 region at night.

The lights were good on the N.S.U. and the vision-field was flat, wide and clear of reflector-fault. The speed was moving through 135 when I took a look and the dipped lamps of the Mercedes were rising slowly to the top of the mirror as the gap widened. Then they switched to full beam and caught me across the eyes and I tilted the glass and drew into the middle area to wait for reaccommodation.

The autobahn ran dead straight in this section and the moon's glow defined it as far as the horizon. There was nothing to do yet except let the engine take her up to the maximum and hold her there. The one trick I could hope to pull off must be kept for emergencies and there weren't any emergencies for the moment The first thing to do was test out the figures I'd been working on: if they were both heavy men and their tank was nearly full then I was going to consolidate the lead I already had on them and peel off as soon as I was out of sight. Then I would put a call through to Ferris while the engine cooled down.

Half a minute later the N.S.U. reached her maximum. The pointer just went up to the 180 k.p.h. mark and stayed there. With this engine there were no valves so there was no indication of bounce; it was purely a matter of starvation: the combustion-chambers were being swept at the speed above which the mixture didn't have time to go in.

The steering was still dead positive and when I moved the wheel a degree she came back correctly without any yawing. I couldn't test for brake-fade because I wanted to know if the 300 could close the gap. The cockpit was full of light but I couldn't tell if it were getting brighter: the reference was too vague.

The dread had passed. Perhaps it had been automatically set up by the organism in its own defence. The situation was dangerous and could be mortal but the necessity of working out the mechanics hadn't allowed the onset of normal fear: and a situation becomes more dangerous if there is no fear present to alert the nerves and prepare the body. Blood should be drawn to the internal organs, draining, from the digestive and secretory glands and skin by contraction of the arterioles so that the heart, brain and muscles can be fed. Breathing should quicken so that the muscles can be given an oxygen reserve. The eyes should dilate, admitting more light.

The human body is no fool but these days it's a little old-fashioned: the defence mechanism set up to dodge the swing of a dinosaur's tail is less effective when life or death depends on the position of a needle on 4 speedometer. But I may well have been, by some small degree, better prepared for action now that the fit of dread was over. It had been the most the organism could do.

Within the next kilometre the first results came in:.the light was stronger inside the cockpit and when I tilted the mirror the back-glare was painful. They were closing the gap.

It wasn't going to be so easy, ringing Ferris.

We passed a truck and I felt the slight air-buffeting as the slipstreams merged and just for an instant I took my foot off but it was already too late: I couldn't slow hard enough to take up a position in front of the truck and use it as a shield. The Mercedes would slot into the gap and the truck itself would become part of the pattern and I didn't want that because they wouldn't have any scruples. Even a twenty-ton twelve-wheeler could be sent off the road if the driver was baulked and I didn't know how hard the Mercedes was going to try when it came to the in-fighting. They had to make it look like an accident and an overturned truck wouldn't detract from appearances.

The inside of the N.S.U. went dark. They'd been overhauling me progressively at 5 or 6 k.p.h. and when I'd taken my foot off for an instant it had closed the gap and brought them right up and they'd cut their lights. The mirror showed a vague dark shape with the glint of chrome in the moonlight. Above the wind-rush I could hear their engine. The needle was steady on 180 and I drew to the crown so that I would have room to manoeuvre when they started.

There was the temptation to hit the brakes and make contact just to surprise them but at this speed it could be immediately lethal. We were covering a hundred yards in two seconds and if the huge weight of the Mercedes didn't make a direct strike on the fore-aft axis of the N.S.U. it would send it off-centre and no amount of steering would bring it back.

Perhaps they were expecting me to do something like that. They didn't mind how it happened, whether it was the result of action on their part or retaliation on mine: providing I jumped the crash-barrier in a series of barrel-rolls and finished up ablaze in the trees down there it wouldn't matter to them how it was done.

It looked very wide in the mirror, very black, a dark wave surging behind me. I was waiting for the nudge and I had to guess which side they'd go for. So long as it wasn't dead central it would work well enough: the smallest impact to one side would send me out of control.

Sweat began again but this was normal: I was in a trap and couldn't get out, couldn't go faster or slower or steer my way clear. A curve came and the crash-barrier uprights sent a flickering echo against the windows and then they made their first strike and the shock went through the body-shell into my seat and as soon as the line was corrected I felt for the safety-belt and clipped it home and.,set the driving-door to locked.

Far ahead in the moonlight a blob showed on the ash-white strip of the road and I hit the horns and kept them blaring because he was too near the crown and I couldn't slow: the next strike or the one after that would throw the whole thing wild and I didn't want to take anyone with me.

It was an Opel Rekord and he pulled over to let me through and then flicked his lights in protest. They made a feeble semaphore in the mirror with the reflection glancing off the mass of black cellulose behind me. Then they tried again and the sweat broke out because the N.S.U. was into a series of oblique lunges before I could correct. The headlamp beams swept the road with the slow regularity of windscreen-wipers and a shrill came from the tyres as traction tried to damp out centrifugal force. Something pattered on the body and hit the left side of the screen with the sound of sudden hail: the nearside front wheel was running off the edge of the concrete and fragments of gravel were shooting up clear of the wing, curving and falling into the slipstream.