David Greig’s delightful Midsummer (a play with songs), opened at the Traverse in Edinburgh in 2008, was revived for last year’s Fringe and now provides a warming tonic for frozen winter nights in London. A knowing, modern romcom about two thirtysomething lost souls from opposite ends of Edinburgh who find each other over the midsummer weekend, it could just as easily serve as a love-letter from the playwright to the city of his birth.