In 1916, Arthur Eddington, a war-weary British astronomer, opened a letter written by an obscure German professor named Einstein. The neatly printed equations on the scrap of paper outlined his world-changing theory of general relativity. Until then, Einstein’s masterpiece of time and space had been trapped behind the physical and ideological lines of battle, unknown. Many Britons were rejecting anything German, but Eddington realised the importance of the letter: perhaps Einstein’s esoteric theory could not only change the foundations of science but also lead to international co-operation in a time of brutal war. We usually think of scientific discovery as a flash of individual inspiration, but here we see it is the result of hard work, gambles, and wrong turns – in this case subject to the petty concerns of nations, religions, and individuals.