While the mountains were in view Pyxeas peered from the yurt, his rheumy eyes squinting in the chill of the breeze, sketching, making notes, muttering, frustrated at how little he could see. ‘The glaciers are growing,’ he told Avatak. ‘Harbingers of the coming of the longwinter. Any record of their growth is useful.’

‘It is like home,’ Avatak ventured. ‘We have such mountains. The ice, the white.’

‘Of course you do. I saw them. But here the cold mantles the mountain because of altitude rather than latitude. By which I mean . . .’

But Avatak wasn’t listening. He had been trying to express his mild homesickness, rather than ask for a lesson on the nature of ice and cold.

‘Oh, do shut that flap,’ Rina complained. ‘You’re letting all the heat out. I don’t know why in the mothers’ mercy you’re carting that Coldland boy along with you. You’re going east, not north. You could hardly choose a less suitable companion. I mean, listen to him. That dreadful guttural language – those words as long as a book! Everybody’s been staring since Parisa.’

‘None less suitable? On the contrary.’ Pyxeas pulled back into the yurt. ‘He is entirely suitable for the role. It’s precisely because this boy is so far from his home environment that he fascinates me so – he demonstrates the suppleness of the human mind. And he is my reserve. Like the second walking stick I have packed in my luggage.’

‘Walking stick? What on earth are you talking about, Uncle?’

But Pyxeas wouldn’t say, and Avatak didn’t know what he meant, and the talk petered out.

The journey had been untroubled save for one mechanical failure, a half-day lost while a split boiler had been welded. But now a new problem arose, with the iron road itself. The caravan was halted and scouts ran ahead.

Rails were missing; even some of the rows of wooden slats pressed into the ground to support the rails had been removed. The workers and engineers gossiped in a dozen tongues. Avatak learned that the theft of rails was becoming more common. These were turbulent times, the country full of raiders and nestspills. Though a rail took some organisation to lift and carry away, its iron could be sold on, or turned into weapons, or put to a hundred other uses. And as the weather turned colder the wood from the support beds was valued as fuel. Alternatively, sometimes bandits would lift a rail or two in order to stop a caravan and raid it.

But the problem could be fixed. Avatak was astonished to discover that one of the caravan’s massive freight wagons was loaded with spare rails, and another with wooden slats for the base. The engineers called for volunteers from the passengers to help with the reconstruction, and Avatak, feeling restless after his immobility in the yurt, stepped forward readily. The work, quickly organised, was heavy but easy: lug the rails and supports from the carriages, push the supports into the soft ground, lay the rails down with careful levelling by the engineers with their plumb lines and water gauges, and hammer home massive rivets. The guards kept up diligent patrols.