Karel Szymanowski’s 1924 opera Król Roger is surely the only opera in Polish in anything like the standard rep. Maybe that’s one reason it’s not performed all that often because it’s really rather good and Kasper Holten’s 2015 production at Covent Garden makes a pretty good case for it. The story is set in 12th century Sicily, though as we shall see , that really doesn’t matter. The Church is complaining to the king about a heretical prophet, the Shepherd, who is leading people astray with a strange doctrine of Love and Nature. Roger’s queen is much taken with the Shepherd and helps protect him. The king, who is clearly battling demons rooted in a bloody past, vacillates. Eventually he’s persuaded and the opera closes with Roger singing an ecstatic hymn to the rising sun.