Alan Ayckbourn, the much-vaunted "Sage of Scarborough", is often hailed as England's greatest living dramatist.

Acclaimed (particularly by the London critics) he may be, but the problem with Ayckbourn is that he is trapped between a desire to be profound and the exigencies of light entertainment.

Even at his best (and Woman In Mind, presented here in an accomplished co-production by Dundee Rep and Birmingham Rep, is among his best), Ayckbourn is a tease. He takes us to the end of the lane, but no further. He gives us good reason to believe there is deeper, darker, more interesting material round the corner, but refuses resolutely to take us there.

In Woman In Mind we find ourselves in parallel worlds. The first is the dull, middle-class existence of Susan, whose marriage to Gerald, a vicar, is hopelessly broken, and whose son is embedded in a cult. The other is the fantasy - induced by unhappiness and a blow to the head - in which Susan belongs to a very rich, very loving, but increasingly sinister bourgeois family.

The shifts back-and-forth place particular demands on the actress playing the titular lead. Fortunately, director Marilyn Imrie's production boasts, in Meg Fraser, one of the finest Scottish actors of her generation. Whether it is Susan's moments of lucid, furious anguish or a sudden, fearful collapse into confusion, Fraser is absolutely captivating.

She receives strong support from a fine cast, not least Neil McKinven as Bill, Susan's perplexed and enamoured doctor. Whether the play, which, typically of Ayckbourn, swings between intriguing psychological drama and sometimes facile humour, deserves all this good work is a moot point.