Why did he do it? Why did Pope Benedict XVI, that most traditional of pontiffs, break with tradition and resign in 2013, ceding the way to his reformist rival, Cardinal Bergoglio? That’s the problem at the heart of this compelling new problem play by Anthony McCarten — and, sensibly, the playwright leaves it more or less unsolved. He presents us with two contrasting and eternal characters, both at breaking point: the wavering conservative and the reluctant liberal. The playwright’s own sympathies seem to be with Bergoglio, yet, despite the relatable ordinariness Nicholas Woodeson brings to that role, it is Anton Lesser’s shy, candyfloss-haired Benedict who, against the odds, emerges as the more fascinating presence: the one who can play Mozart, however imperfectly, the one who attempts little jokes, far less polished than his rival’s hail-fellow shtick, yet more amusing for their faults. McCarten, who wrote the screenplay for Darkest Hour, has a gift for creating intimate dramas from public biographical property. Here the theatre becomes a confessional, with the audience asked to grant absolution to two flawed but pious priests.