On the eve of the Great War, they had the world at - and watching - their feet. If God is in the details, they were divine. Vernon and Irene Castle were the world's first true celebrity couple. He, an Englishman, was tall and slim, as poised as an elegant evening out, a template for the Hollywood idols who would follow. In a staid age, she, a New Yorker, was a glorious, modern beauty, with her haired cropped into a 'shock', a disdain for crippling corsets, a love of a martini and a good time. To