Crimm bent, dug in a locker to retrieve an axe, then clambered up the main mast by the rigging and began to hack at the ice sheets. Another man, he couldn’t see who, was doing the same at the stern mast. His hands were quickly going numb, and he thought of digging out his mittens, but he wouldn’t be able to hold the rigging firmly enough. The boat rolled in a swell, and the men skidded over the deck. Crimm had to wrap an arm around the main mast and nearly lost his grip on the axe.

And the man at the stern dropped from the mast, slid over the slick deck, fell into the surging water, and was gone in an eye blink.

The storm blew over as quickly as it had come upon them. The crew slumped on the deck, exhausted, their breath billowing before their faces. The air felt much colder than before the storm had passed, and Crimm could see the residual wet on the deck frosting up. Suddenly they had sailed into winter.

He worked his way around the ship, passing out water bags and lumps of dried fish, and quietly counted the men. Seven of them left, one lost. He organised a couple of them to start pumping out the bilge, which was awash with icy water.

‘We lost Xon,’ a man called Aranx murmured.

‘Yes. Only sixteen, wasn’t he?’

‘Seventeen.’

‘I’ll tell his mother when we get back.’

‘I’ll do it,’ Ayto said. ‘I play knuckles with the father. The stern mast’s snapped, by the way. That’s the main damage. That and a hundred leaks.’

‘We can lash the mast,’ Crimm said. When they got back to the Wall the other damage would be straightforward to repair; the boat’s construction was planking laid over a sturdy skeleton, and replacing sections was easy in dry dock.

There was a scraping along the hull, as if they had struck a reef.

Ayto, Crimm and Aranx glanced at each other, and hurried to the rail.

The ice was floating in cakes around them, flat, thick, some of them slushy. The scraping they had heard had been one of the cakes brushing past the stern. The floes looked like lilies on some dismal, colourless pond, Crimm thought.

‘In this cold that lot is going to thicken quickly,’ Ayto said.

‘We can get through it for now.’ The Sabet’s high prow was designed to help it weather heavy seas. It was good at pushing through loose surface ice like this. ‘Break out the oars. If it goes on long enough we’ll rotate the man at the rudder.’

‘All right.’

Soon they had the crew organised, and rowing steadily. Crimm worked the rudder for a time, then tied it up and went to work at the bilge pump.