Midsummer, Soho Theatre

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.

You don’t have to know Scotland’s capital to follow the plot, but you will get more laughs out of the evening - many of them wry - if you do (and anyway, a map is thoughtfully provided). Being midsummer, it is of course pouring down in Auld Reekie, with a nasty haar (a posh fog, the writer tells us) and, despite living in Britain's most captivating city, Helena and Bob are not what you might call beautiful people. She’s a divorce lawyer in a dead-end affair with a married man, he’s a small-time criminal with a great future behind him. He wanted to be a poet, and now reads Dostoevsky for pleasure.

Helena and Bob meet in a wine bar where she has been stood up by her marrried man and he is about to offload a hot motor, and their drunken one-night stand turns into a lost weekend. The play goes back and forth in time over the weekend, scenes are replayed after we hear the addition of Helena and Bob’s inner thoughts, and Cora Bissett (as Helena) and Matthew Pidgeon (Bob) play other incidental roles. They also provide much of the soundtrack as they, boulevard-style, strum guitars and sing songs (written by Gordon McIntyre) at regular intervals, but it’s never cheesy, and Greig, who also directs, keeps the pace rattling along.

There is only one scene that jars, when the actors break the fourth wall and there’s an awkward piece of audience participation. It interrupts our rapt attention as the lovers become embroiled in a rollicking good story that details a pregnancy test, trips to Ikea and a bondage club, a cathedral wedding involving a vomit-strewn 12-year-old, some stolen money and the goths who hang out in Princes Street Gardens.

Greig also injects enough gimlet-eyed realism to keep the schmaltz at bay. Helena and Bob are both flawed characters and, although we know they will end up together (ish), their journeys - literal and figurative - are believable and sympathetic. Bissett and Pidgeon are superb as the lovers and Midsummer is a feelgood treat.

Midsummer booking at the Soho Theatre, London until 6 February