This hour it was Thaxa’s turn to make the piss run.

He rose from the corner of the huge old cistern, where he’d been reading a scroll by the dim light that came down the air shaft at midday. It was the only light in the room save for the increasingly rare intervals when they lit the lamps. He stood and pulled on his outer clothes, his heavy hooded coat and his waterproof leather trousers and his boots.

Then, carefully avoiding the prone bodies on the floor, he made for the door leading to the passages out to his house at the face of the Wall. It was the time of day when the small children were laid down together to nap. ‘Time to sleep now,’ the mothers were whispering all across the chamber. ‘Time to sleep.’ Some of the adults slept too, if they could, in the muggy air. Sleep was the best way, the only way really, to use up the empty, pointless hours in this growstone box. There was the usual stink of fish, their staple food, on their breath and in their farts, though you would think he would have got used to that by now. In the dimness he recognised Crimm the fisherman, a few other faces.

The people here were not exactly friends; the jealousy over food and floor space was too strong for that. But they were his guests, that was how he thought of them. He had been astonished to learn from Crimm and Ayto that this huge abandoned cistern buried deep within the Wall behind his own house was, in theory, his property. He hoped that if they survived this dreadful winter they would remember his contribution, the last gesture of hospitality from a hospitable man.

At the door he picked up the latest slop buckets. Aranx, the young fisherman who had lost an arm to the frost, was on guard this hour. He offered Thaxa a weapon, a stabbing spear with a rope sling, but Thaxa had never used a weapon in his life and he saw no point in pretending he could now. Aranx shrugged, opened the door, let him pass through, and closed it after him.

After the human fug of the cistern, the corridors and empty rooms he passed through were dark and bleakly cold. In the circle of light cast by his candle, Thaxa walked softly. Crimm and Ayto had endlessly stressed to those who they had brought into this refuge that as the Wall burned itself up this winter their best hope was to stay concealed – not to be discovered at all, because that way they wouldn’t have to fight again, for their food, their lives, as they had had to already.

Ayto himself was waiting for him at the exit from the growstone: another guard on duty, heavily armed with sword and spear and stabbing knife. ‘Go carefully,’ he whispered to Thaxa. ‘And look out for Xree.’

‘Xree? What about her?’