Scarborough, Royal Court, London

Fiona Evans's play Scarborough won a Fringe First at last year's Edinburgh Festival, where it was a talking point because of its subject-matter – a dirty weekend in a Scarborough B&B involving a female PE teacher and a pupil 14 years her junior – and the uncomfortable intimacy of its staging. A tiny space was transformed into a dingy room in a faded seaside guesthouse, with the audience, turned into voyeurs, pinned against the walls.

I didn't see the piece in Edinburgh, so I am glad to catch up with Deborah Bruce's melancholy production at the Royal Court. While you would be capable of swinging a cat in the Theatre Upstairs, an atmosphere of physically and morally awkward closeness has been artfully preserved.

In Jo Newberry's evocatively sad setting, with its peeling floral wallpaper and Charles and Diana wedding plates, there's still a strong sense of strain. Pretending to be invisible in what looks like a case of extreme over-booking, the crammed-in audience violates the privacy of the unsuspecting pair.

A new twist, though, has been added to the play since Edinburgh. There is now a second half in which the 40-minute drama from before the interval is reprised in its entirety, except that the PE teacher is now male and the pupil female.

All four actors – Holly Atkins and Jack O'Connell to begin with; Daniel Mays and Rebecca Ryan in the gender-reversed re-run – give truthful performances that hit bang-on the notes of bleak, bantering comedy and encroaching desolation. If I found the first half more moving, it was because I wondered whether this about-face repetition has any deep diagnostic value.

O'Connell's teenage Daz comes across as less emotionally mature than his female counterpart (Ryan). He's a boy trying to act like a man. By contrast, Ryan's pert, glammed-up Beth has a self-possession and a moral power that eventually allow her to sit in judgement over Mays's desperately back-tracking Aiden. There are moments when you might think he was the younger party.

You never get that impression from Atkins's excellent Lauren. She shows you an insecure woman torn between Daz and the older fiancé who (ironically) took over her life while he was her swimming coach. She knows that time is running out, and not only in this doomed affair.

To 8 March (020-7565 5000)