In one corner, a godless young warrior, Voltaire’s heralded ‘philosopher-king’, the It Boy of the Enlightenment. In the other, a devout if bad-tempered old composer of ‘outdated’ music, a scorned genius in his last years. The sparks from their brief conflict illuminate a turbulent age.Behind the pomp and flash, Prussia's Frederick the Great was a tormented man, son of an abusive king who forced him to watch as his best friend (probably his lover) was beheaded. In what may have been one of...