The gun is a People’s Army issue K-54, decades old and feeling worn smooth with age. He has never fired it but it is meant to be reliable. The silencer looks crude, almost home-made. Still, it will have to do. He wipes his hand on his trousers, cocks the gun and extends his fingers towards the code panel above the handle of the door leading to the private carriage. A tiny red light pulses slowly on the lock’s display.

They are approaching the highest part of the line, the Tanggula Pass, still most of a day away from Lhasa. The air feels cool and thin here, five kilometres up. Most people will be keeping to their seats, plugged into the train’s oxygen supply. Outside, the Tibetan plateau – a symphony of dun, beige and brown with a bitty overlay of early-summer green – has ridged and buckled over the last hour to create foothills that harbinge the crumpled parapets of low encroaching mountains in the distance.

The chief train guard had demanded a lot of money for the override code. It had better work. He taps it in quickly.

The tiny pulsing red light turns steady green. He feels himself swallowing.

The train rocks; the handle feels cold beneath his fingers.

And it begins with our young-sounding, young-looking, young-acting but in the end middle-aged friend Mr Adrian Cubbish waking up in his Mayfair home one London morning in – oh, let’s say late summer 2007; the routine is the same for the majority of days. He is in his bedroom suite, which takes up most of what used to be the attic of the town house. A light rain is falling onto the slabs of double-glazed glass which point at forty-five degrees to the light grey sky.

If Adrian were to have a symbol, it would be a mirror. This is what he says to the mirror each morning before he goes to work, and sometimes at the weekends when he doesn’t have to go to work, just for the sheer hell of it: