In a 1980s lecture Iris Murdoch made the telling observation that “in good art we do not ask for realism; we ask for truth”. And it’s a comment worth bearing in mind with Verdi’s Un ballo in maschera (A Masked Ball), playing at the new Grange Park Opera, Surrey. The plot of Ballo culminates in a political assassination, which is realistic enough. But in the process it sails through narrative improbabilities of such contrivance you’d dismiss them as absurd if they weren’t dignified by Verdi’s authorship. In good productions they become acceptable because they ride on the trajectory of music-drama that propels you through events without inviting you to stop and question. And though Stephen Medcalf’s Grange Park show is questionably good (with action relocated to the time of Abraham Lincoln’s America, it’s costume-stiff and downbeat), it works well enough to feel comparatively truthful. There’s a strong cast, with a superb Renato (the assassin) from Roland Wood. And the conductor Gianluca Marciano – an Anglophile Italian who does a lot of work for Grange Park – delivers the energy the staging sometimes lacks, keeping the orchestra of English National Opera (who are moonlighting here for the summer) on their toes. But the big foot-tapping attraction at Grange Park this season is another piece of improbable Americana: Rodgers and Hammerstein’s Oklahoma! Written during World War II as patriotic escapism, it inhabits a world where the nearest thing to crisis is the possibility that two farm girls might end up marrying the wrong men: a Jane Austen narrative, with cattle. That the territory of Oklahoma! at the time we’re in has just been stolen from its Native Indian occupants with tragic consequences gets no mention. But the songs are irresistible, attacking you with feel-good force – as they do here in a production that’s not so slick as you’d find in the West End but joyously alive, with the advantage of a serious orchestra in the pit (the BBC Concert) and the bravery of colour-blind casting. Dex Lee could do with more vocal energy as the chief suitor, Curly, but has presence. And his being black feeds interesting tension into Laurey’s reluctance to have him. If we were really in the still racist rustic America in the early 20th century their union would be unthinkable. Almost equally unthinkable is the speed with which Grange Park Opera has settled into its new home near Guildford. Given that the theatre, built from scratch in record time, opened just last year, it feels well established, thriving, confident: a real achievement, and true testimony to the dynamism of its founder Wasfi Kani. No one else in our depressed, adrift, pre-Brexit Britain could have done it.