"Heaven help them," Joss said soberly. He added something else, but I didn't wait to hear. I wanted to get up top as quickly as possible.

To leave our cabin, we had to use a trap-door, not an ordinary door. Our cabin, a prefabricated, sectioned structure that had been hauled up from the coast on tractor sleds during the month of July, was deep-sunk in a great oblong hole that had been gouged out from the surface of the ice-cap, so that only the top few inches of its flat roof projected above ground level. The trap-door, hinged at both ends so that it could open either upwards or downwards, was reached by a short steep flight of steps.

I climbed the first two of these, took down the wooden mallet that hung there permanently by the wall and pounded round the already bruised and splintered edges of the trap to loosen the ice that held it locked fast. This was an almost invariable routine: whenever the trap had previously been opened for any length of time at all, the layer of warm air that always lay under the roof seeped slowly out, melting the surrounding snow—which promptly turned to ice when the trap was closed again.

Tonight the ice cracked easily. I got my shoulder under the trap, levered upwards against the accumulated drift of snow above, and scrambled out.

I was prepared for what awaited me up top—the gasping, panic-stricken feeling of suffocation as the warm air was sucked from my lungs by that deadly, numbing cold—but even so I wasn't sufficiently prepared. The wind speed was far higher than I had feared. Bent double and coughing violently, breathing shallowly to avoid frosting my lungs, I turned my back to the wind, breathed into my reindeer gloves, slipped on my snow-mask and goggles and straightened. Jackstraw was already standing by my side.