There was no sign of him in the Futures’ room, and so I waited for a while. After half an hour he had still not appeared, so knowing my services could be better employed outside I headed back the way I had come.

I met Future Denton in the corridor.

“You’re Future Mann, aren’t you?”

“Yes.”

“We’re leaving the city. Are you ready now?”

“I was supposed to be seeing Future Clausewitz.”

“That’s right. He’s sent me instead. Can you ride a horse?”

I had forgotten the horses while I was away from the city. “Yes.”

“Good. Meet me at the stables in an hour’s time.”

He walked on into the Futures’ room.

With an hour to spend on my own, I realized that I had nothing to do, no one to see. All my connections with the city were broken; even associative memories of the physical shape and appearance of the city had been disrupted by the damage.

I walked down to the rear of the city to see for myself the extent of the damage to the crèche, but there was not much to see. Almost the whole superstructure had been burnt or latterly demolished, and where the children had been housed was merely the bare steel of the main base of the city. From there I could see back across the river to where the attack had taken place. I wondered whether the tooks would try again. I felt they had been well beaten, but if the city was resented as much as appeared I supposed they would eventually re-form and attack once more.

It came home to me just how vulnerable the city was. Not designed to repel any kind of attack, it was slow-moving, ungainly, built of highly inflammable materials. All its weakest points, the tracks, the cables, the timber superstructure, were easily accessible.

I wondered if the tooks realized how easy it would be to destroy the city: all they needed to do was disable its motive powers permanently, then sit back and watch as the movement of the ground slowly bore it southwards.

I considered this for some time. It seemed to me that the local people did not understand the inherent frailty of the city and its inhabitants, because of the lack of information available to them. As far as I could tell, the strange transformation that had overtaken the three girls down past was subjectively to them no transformation at all.

Here, near optimum, the tooks were not subject to distortion — or only to an indiscernible degree — and so no perception of any difference was possible.

Only if the tooks succeeded, perhaps not even by design, in delaying the city to such a degree that it was borne to a point so far south that it could never haul itself forward again would they see the effect this would have on the city and its occupants.

Under normal conditions, the city would be facing difficult country; the hill to the north of us was probably not the only one in this region. How could it ever again hope to approach the optimum?

For the moment, though, the city was relatively secure. Bounded on one side by the river, and by rising ground which would afford no cover to any aggressor on the other, it was strategically well placed while the tracks were laid.

I wondered whether I had time to find a change of clothes, as I had been working and sleeping in the same ones for many days. This thought inevitably reminded me of Victoria, and how she had objected to my uniform after ten days in it outside the city.

I hoped I should not see her before I left.

I returned to the Futures’ room, and made enquiries. There were indeed uniforms available, and I was entitled to one as I was now a full guildsman… but there was none available at the moment. I was told that one would be found while I was away.

Future Denton was waiting for me when I arrived at the stables. I was given a horse, and without further delay we rode out from beneath the city and headed north.

3

Denton was not a man who would say much unprompted. He answered any questions I chose to ask, but between there were long periods of silence. I did not find this uncomfortable, because it gave me a much needed opportunity to think.

The early training of the guilds still ran true: I accepted that I would make what I could of what I saw, and not rely on the interpretations of others.

We followed the proposed line of the tracks, up around the side of the hill and through the pass. At the top, the ground ran steadily downwards for a long way, following a small watercourse. There was a small patch of woodland at the end of the valley, and then another line of hills.

“Denton, why have we left the city at this moment?” I said. “Surely every man is needed.”

“Our work is always important.”

“More important than defending the city?”

“Yes.”

As we rode he explained that during the last few miles the future-surveying work had been neglected. This was partly because of the troubles, and partly because the guild was undermanned.

“We’ve surveyed as far as these hills,” he said. “Those trees… they’re a nuisance to the Track guild, and they could provide cover for the tooks, but we need more timber. The hills have been surveyed for about another mile, but beyond that it’s all virgin territory.”

He showed me a map that had been drawn on a long roll of paper, and explained the symbols to me. Our job, as far as I could tell, was to extend the map northwards. Denton had a surveying instrument mounted on a large wooden tripod, and every so often he would take a reading from it and make inscriptions on the map.

The horses were heavily laden with equipment. In addition to large supplies of food and bedding, we were each carrying a crossbow and a good supply of bolts; there was some digging equipment, a chemical-sampling kit, and a miniature video camera and recording equipment. I was given the video kit to use, and Denton showed me how to operate it.

The usual method of the Futures, as he explained it to me, was that over a period of time a different surveyor, or a different team of surveyors, would move north of the city by different routes. By the end of the expedition he would have a detailed map of the terrain through which he had passed, and a video record of its physical appearance. This would then be submitted to the Council of Navigators and they, with the help of other surveyors’ reports, would decide which route would be taken.

Towards late afternoon, Denton stopped for about the sixth time and erected his tripod. After he had taken angular readings on the elevation of the surrounding hills, and, by use of a gyroscopically mounted compass, had determined true north, he attached a free-swinging pendulum to the base of the instrument. The weight of the pendulum was pointed, and when its natural momentum was spent and the pointer was stationary, Denton took a graduated scale, marked with concentric circles, and placed it between the legs of the tripod.

The pointer was almost exactly above the central mark.

“We’re at optimum,” he said. “Know what that means?”

“Not exactly.”

“You’ve been down past, haven’t you?” I confirmed this. “There’s always centrifugal force to contend with on this world. The further south one travels, the greater that force is. It’s always present anywhere south of optimum, but it makes no practicable difference to normal operations for about twelve miles south of optimum. Anything further than that, and the city would have real problems. You know that anyway, if you’ve felt the centrifugal force.”

He took further readings from his instrument.

“Eight and a half miles,” he said. “That’s the distance between here and the city… or how much ground the city has to make up.”

I said: “How is the optimum measured?”

“By its null gravitational distortions. It serves as the standard by which we measure the city’s progress. In physical terms, imagine it as a line drawn around the world.”