By the time they had disentangled, got dressed, and returned to the tent, Rosario and Lucia were eating a pile of yellow gruel. Neither of them said anything, but Helward saw Lucia smile at Caterina.

Half an hour later the baby was sick again… and as Rosario was holding it concernedly, she suddenly thrust the baby into Lucia’s arms and rushed away. A few seconds later, she could be heard retching beside the stream.

Helward said to Caterina: “Do you feel O.K.?”

“Yes.”

Helward sniffed the food they had been eating. It smelt normal… unappetizing, but not tainted. A few minutes later, Lucia complained of intense stomach pains, and she went very pale.

Caterina wandered away.

Helward was desperate. The only course open to them now seemed to be to return to the city. If their food had become foul, how would they survive the rest of the journey?

After a while, Rosario returned to the camp-site. She looked weak and pale, and she sat down on the ground in the shade. Lucia gave her some water from the canteen. Lucia herself looked white and was holding her stomach, and the baby continued to scream. Helward was not prepared to cope with a situation like this, and hadn’t the least idea of what to suggest.

He went in search of Caterina, who had seemed to be unaffected.

About a hundred yards down the chasm he came across her. She was walking back towards the camp-site with an armful of apples which, she said, she had found growing wild. They looked red and ripe, and Helward tasted one. It was sweet and juicy… but then he remembered Clausewitz’s warning. His reason told him Clausewitz was wrong, but reluctantly he gave it to Caterina and she ate the rest.

They baked one of the apples in the embers of the fire, and then pulped it. In tiny mouthfuls, they fed it to the baby. This time it kept the food down and made happy noises. Rosario was still too weak to attend to it, so Caterina laid it down in its cot and within minutes it was asleep.

Lucia was not sick, although her stomach continued to give her pain for most of the morning. Rosario recovered more quickly, and ate one of the apples.

Helward ate the rest of the yellow synthetic food… and it did not make him ill.

Later in the day, Helward climbed up to the top of the creek and walked along its northern side. Here, a few miles back in time, lives had been lost in the cause of getting the city to cross this chasm. The scene was still familiar to him, and although most of the equipment used by the city had been collected, those long days and nights spent racing to complete the bridge were still very vivid in his memory. He looked across to the southern side, at the very place where the bridge had been built.

The gap did not look as wide as it had done then, nor did the chasm look so deep. Perhaps his excitement at the time had exaggerated his impression of the obstacle the chasm presented.

But no… surely the chasm had been wider?

He remembered that when the city had been crossing the bridge the rail-way itself had been at least sixty yards long. Now it seemed that at the point the bridge had been built the chasm was only about ten yards wide.

Helward stood and stared at the opposite edge for a long time, not understanding how this apparent contradiction could occur. Then an idea came to him.

The bridge had been built to quite exact engineering specifications; he had worked for many days on the building of the suspension towers, and he knew that the two towers on each side of the chasm had been built an exact distance apart to allow the city to pass between them.

That distance was about one hundred and thirty feet, or forty paces.

He went to the place where one of the northern towers had been built, and walked over towards its twin. He counted fiftyeight paces.

He went back, trying again: this time it was sixty paces.

He tried again, taking larger steps: fifty-five paces.

Standing on the edge of the chasm he stared down at the stream below. He could remember with great clarity the depth of the creek when the bridge was being built. Standing here, the bottom of the chasm had seemed to be a terrifying depth below; now it was an easy climb down to where they had camped.

Another thought struck him and he walked northwards to where the ramp had brought the city down into contact with the soil again. The traces of the four tracks still showed clearly, from this point running parallel northwards.

If the two towers were now apparently further apart, what of the tracks themselves?

From long hours working with Malchuskin, Helward knew intimately every detail of the tracks and their sleepers. The gauge of the tracks was three and a half feet, resting on sleepers five feet long. Looking now at the scars left in the ground by the sleepers, he saw that they were much bigger than this. He made a rough measurement, and estimated that they were now at least seven feet long, and shallower than they ought to be. But he knew that could not be so: the city used standard length sleepers, and the pits dug for them were always roughly the same size.

To make sure he checked several more, and found they were all apparently two feet longer than they should be.

And too close together. The sleepers were laid by the trackcrews at four feet intervals… not about eighteen inches apart, as these were.

Helward spent a few more minutes making similar measurements, then scrambled down the chasm, waded through the stream (which now seemed to him to be narrower and shallower than it had been before), and climbed up to the southern edge.

Here too the measurements he made of the remains of the city’s passage were in stark conflict with what he knew should be so.

Puzzled, and more than a little worried, he returned to the camp.

The girls were all looking healthier, but the baby had been sick yet again. The girls told him that they had been eating the apples Caterina had found. He cut one in half, and inspected it closely. He could see no difference between it and any other apple he had ever eaten. Once again, he was tempted to eat it, but instead he passed it to Lucia.

An idea had suddenly occurred to him.

Clausewitz had warned him of eating local foods; presumably this was because he was of the city. Clausewitz had said it was all right to eat local foods when the city was near optimum, but here, some miles to the south, it was not so. If he ate the city food, he would not be ill.

But the girls… they were not of the city. Perhaps it was his food which was making them ill. They could eat city food when they were near the optimum, but not now.

It made a kind of sense, but for one thing: the baby. With the exception of the few tiny mouthfuls of apple, it had had nothing but its mother’s milk. Surely that could not harm it?

He went with Rosario to see the baby. It lay in its cot, its face red and tear-stained. It was not crying now, but it fretted weakly. Helward felt sorry for the tiny creature, and wondered what he could do to help.

Outside the tent, Lucia and Caterina were in good spirits. They spoke to Helward as he emerged, but he walked on past them and went to sit beside the stream. He was still thinking about his new idea.

The only food had been its mother’s milk… Suppose the mother was different now, because they were away from the optimum? She was not of the city, but the baby was. Could that make a difference? It did not make much sense — for surely the baby was of the mother’s body? — but it was a possibility.

He went back to the camp and made up some synthetic food and dried milk, being careful to use only water he had brought from the city. He gave it to Rosario, and told her to try feeding the baby with it.

She resisted the idea at first, but then relented. The baby took the food, and two hours later it was sleeping peacefully once more.