Ten per cent … It seems a small number. I frown, trying to work out if I’m one of them. As the ground falls away I glance through the window, watching the world shrink, snow-capped mountains suddenly dominating the view. There’s a chime as the seat belt sign goes off and I get up, glancing for a moment down the length of the aircraft. One hundred and twenty-three faces that can see my neatly pinned-back hair, my mask of immaculate makeup, my navy uniform dress and smart shoes. One hundred and twenty-three lives I know nothing about, just as they know nothing about mine.

As I set up the drinks trolley, the statistic on the magazine cover stays with me, and I think about how many people who, for all kinds of reasons, cause suffering to others. I used to believe that even the worst behaviour could be explained by abusive childhoods or desperation. But that was before I realised people have choices; make decisions. Before I realised that brutality can be intentional.

The passengers are mostly students in big coats and trainers, blank-faced business travellers, and wealthy Italians in designer wear. As I serve cups of tea, I usually imagine them to be parents, families, friends, vacationers. But none of us knows what lies behind appearances, or what we’re capable of in extreme circumstances. As I look at them I’m wondering which of them are in the ten per cent – out of one hundred and twenty-three, that’s only twelve or thirteen – but it’s impossible to tell.

Now and then, I catch a glimpse through a window of the bird’s eye view of which I never tire – a view of a world that’s endlessly beautiful. At thirty-five thousand feet, you see the landscape in large scale: stretches of sea, jagged mountain ranges, hundreds of miles of patchwork farmland. Today, beneath a pale blue sky, the mountains have given way to a sea of snow fields, broken here and there by a circular town or a spider’s web of serpentine roads; by monolithic chimneys from which vertical smoke rises, scored into the whiteness. Over northern France, the snow reduces to an icing-sugar dusting. Then, as we start our approach into London and I go through the cabin checking seat belts, the clouds thicken and the reality of my life on the ground comes flooding back.

*