To get the feel of the polar night, I went back to Spitsbergen in winter. I went snowshoeing in the dark and experimented with headlamps and climbed a glacier in driving snow.

I've climbed Stromboli when it's erupting, which is quite a heavy climb: three hours with a helmet to get to the top. When you're there, and it's dark, and you can see this eruption and feel it, it's quite different to watching it on TV.

"Snow was falling,
so much like stars
filling the dark trees
that one could easily imagine
its reason for being was nothing more
than prettiness.

It's true to say that once I've got the bare bones of a story, I often get ideas from my own research trips to faraway places.

I'm quite happy trekking around Greenland on my own, but those big book tours in America or the Far East are the only time I ever really feel lonely.

For a novelist, the great thing about the Stone Age people is that we know virtually nothing about their beliefs - which means that I get to make it up! But it's still got to be plausible.