At heart, of course, Larraín and Knight’s tale is utterly preposterous. It’s a tragedy about a spoiled princess who lashes out at the servants; a thriller about a woman who has only 10 minutes to get into her dress before Christmas dinner is served. But how else do you play it? The monarchy itself is preposterous. Spencer presents the whole institution as little more than a silly ongoing game of dress-up, a farce that depends for its survival on everyone playing along and propping up the illusion, the old moth-eaten brocade. Anybody who doesn’t is ostracised, crushed or cast out in the cold, with the scarecrow and the pheasants and the shivering security men. “Will they kill me, do you think?” says Diana, half-joking, and such is the level of fury and tension that just for a moment we believe that they might.