In 1974, Terence Rattigan wrote a television script for the BBC about the relationship between Diaghilev, the impresario behind the Ballets Russes, and Nijinsky, the most renowned dancer of all time, which Rattigan described as "the greatest love story since Romeo and Juliet." But the playwright withdrew the play and it was never produced. Now in this bold re-imagining of events, Nicholas Wright investigates why.