It wasn’t an impossible job. The system, already centuries old, had evolved with time for ease of repair. Lying flat, he could reach down to the broken section. He checked that his rope harness was fixed securely to a stout rung, and then dug out a wrench and a short length of brass sleeve that he would use to join the broken ends of pipe to make a temporary fix. The welders could come up here and make the joint good when the weather relented. He flipped back his mittens’ lids to expose his fingers, taking care not to touch the still-hot pipes, and grabbed the broken section with his right hand.

As his hand closed around the freezing metal he knew immediately he’d made a horrible mistake.

The agonising cold sank into his fingers and palm. When he tried to loosen his fingers he found the flesh was glued firmly to the metal surface. He tried harder, and he could feel the flesh tear, and blood oozed out onto the metal where it froze immediately, a glistening crimson. He was stuck. Lying here face down on the growstone, his right arm outstretched down the Wall, he couldn’t even reach the locked right hand with his left. Be careful, his mother had always said. One mistake out there – that’s all it will take. And she’d been right. This had been that one mistake, for him.

He could feel the cold penetrating through his hand, up his arm. The wind picked up again and blew back his hood from his head, so his face and scalp were exposed to the driving snow. The flakes were heavier now, harder, and they stung as they slapped at his skin. He could feel ice on his face, below his eyes. He couldn’t tell if he was crying or not. He was going to die out here, he realised. It wasn’t just that he’d messed up the job. He would freeze to death, trapped like an idiot up on this Wall. He tried again to force open his fingers, but again he felt flesh rip, and what felt like a web of muscles beneath the skin tearing. The pain was astounding. He slumped back, exhausted, defeated, agonised. He yelled into the wind: ‘How could I be so stupid?’

‘Good question!’ It was his mother’s voice. Kia was lying face down by his right-hand side, bundled up in her own furs.

‘You shouldn’t be up here.’ His teeth were chattering.

‘No, I shouldn’t. And I shouldn’t have given birth to an idiot like you. But one thing follows the other, doesn’t it?’ She pulled his hood back over his head, and kissed him on an exposed bit of forehead. ‘Now hold still or you’ll pull that hand to bits.’ She dug her own bare fingers into a pot of oil and reached down and began to massage the fingers and palm of his locked hand.

‘What is that?’

‘Sperm-whale oil. Had it in the store for years. Old Coldlander trick, although they say seal oil is the best. It’ll take a little time but we’ll get you free. Leave it to Mother.’