Playwright Simon Gray likes to return to the staff common rooms he inhabited during his years as a university lecturer, and the on-stage action of his 1981 comedy Quartermaine's Terms takes place entirely in this not so holy of holies.

In the common room of a private language school for overseas students - which does at least boast a prestigious Oxbridge address - we follow the eponymous Quartermaine, a likeable though ineffectual middle-aged teacher, through the terms of the college year. He cuts a lonely figure, with no life outside the staff room, except where he's needed to babysit or act as foil in the domestic upheavals preoccupying his colleagues.

The play is notable for its vividly realised cast of off-stage characters. There are the pupils, of course, heard and not seen. There are the families of Quartermaine's colleagues, including a hateful invalid mother, depressive teenage daughter, cheating husband and missing wife. And, looming in the background is Thomas, the partner in all senses of Eddie, who runs the language school.

Simon Godwin's production handles these relationships with great delicacy and a marvellous feel for the play's early 1960s setting. In this, he's well served by David Farley's striking set, both realistic and symbolic, with French windows opening onto the sunshine of a world beyond the staff room.

The cast is uniformly excellent, inhabiting the set - and their costumes - with a fine sense of period speech and movement. Rupert Wickham is quietly heartbreaking as Quartermaine, almost imperceptibly slipping into irreversible decline.

And around him the rest of the cast succeeds in the difficult task of making us believe in the people we never meet, who have such an effect on their lives. Josh Cohen makes a convincingly earnest and obsessive would-be novelist. Sophie Shaw blossoms nicely from being the thinking man's crumpet in this staff room into a proto-feminist.

Timothy Davies' tweedy senior lecturer is wonderfully English in his stoicism, and Melanie Garth gives a fine study of a highly intellectual, unfulfilled middle-aged spinster. Ian Price finds just the right over-the-top status as the Head, and newcomer Jonas Armstrong provides the comic turn of the evening as the accident-prone and earnest rookie teacher.

Quartermaine's Terms winds down to something of an unsatisfactory ending, which, on the night I saw it, left the audience unsure of when to applaud. But this dissection of middle-class intelligentsia brings its own quiet rewards.

- Judi Herman (reviewed at Northampton's Theatre Royal)