The US playwright's new drama, at the Old Vic in London, is a tragicomic romance amid swastika-shaped flowerbeds. She talks about finding a dark past on a trip to Long Island In May 2020, the playwright Bess Wohl rented a house in Bellport, Long Island, a bayside village an hour or two from Manhattan. This was during the early months of the pandemic, when Wohl found herself running an impromptu summer camp for her th…