RELATIVELY SPEAKING is basically a modern-day farce, with mistaken identity being the pivot around which all the shenanigans turn. It’s the theatre’s equivalent of a chain reaction and there’s no stopping it. The characters wend their way through conversations with the propriety of Queen Victoria and the concentration of Houdini, only to come up with the most erroneous conclusions about one another. The play starts with a genial young couple who have been living together for a month in her London flat, and the young man has even broached marriage. But there’s one matter she must dispose of first and she’s off to the country to visit her parents for the day. That’s what she says. Assumptions are multiplied ten-fold, and that’s the whole funny business.