For a long time I’ve been fascinated by the true story of Hermann Muller, the American geneticist who demonstrated the link between radiation and genetic mutations. In his attempt to work in a place where he wouldn’t be persecuted for his Communist beliefs, he travelled from Texas to Nazi Germany, to Stalin’s Soviet Union, to war-torn Spain, and finally found refuge in Edinburgh. My story ‘Lord of the Fruit Flies‘, which was specially commissioned for BBC Radio 4, imagines this last train journey north to Scotland, as he travels with his most precious cargo – a suitcase full of genetically modified fruit flies.