My duties as a secret agent charged with recovering a sacred text were part-familiar and part-terrifying. As I stood on the pavement on Edinburgh’s George Street, I knew that the passing motorcyclist would slap me when he drove past. Then I would run into the Halifax bank to seek shelter. Everyone would believe that a terror attack was imminent.

The next day I walked along the banks of the River Thames at sunset. My assailant, carrying the quarry, had followed me to the capital. I almost fell into the water as I reached down to grab the precious book from him.