If you want to appreciate why the return of Twin Peaks is so significant, then you need to know something of the background. And, no, not the background of the show itself, which rose and fell through two series before coming to a stop on 10 June 1991. Nor the background of its story, which began with the sodden corpse of Laura Palmer and concluded with the FBI agent Dale Cooper — or was it? — smashing his head into a mirror.