THEATRE / Take a hint: Robert Hanks reviews The Grapes of Wrath at the Shaw Theatre

It's sad watching 7:84 Scotland perform The Grapes of Wrath: sad not just because of what goes on on stage - although Steinbeck's story of Okie farmers heading to California in search of work still has a tragic sweep that carries you along - but because the unambiguous politics of the play have been thoroughly marginalised. So that what might have been powerfully political theatre a decade ago now sounds remarkably like whistling in the dark.

The other distressing thing about this co-production with Dundee Rep is that it has been marooned on the stage of the Shaw, one of the most inhospitable barns in London. The quietest moments are invaded by the hum of the air-conditioning, while the big set-pieces are muffled by the shrouding acoustic.

Iain Reekie's production pulls through in the end, but it's a long haul. The fault lies partly in the adaptation, by Frank Galati, which allows even the central characters little space to develop, and gives too much elbow room to ex-Reverend Casy's speeches expounding his new pantheistic, quasi-socialist mysticism.

None of the characters has any hinterland beyond their bare function in the plot: Rose of Sharon is there to be pregnant, for instance, so Julie Duncanson spends most of her time just clutching her midriff and waddling. Even Anne Kidd's strongly etched Ma Joad works more as a reminder of what a determined, upright woman might be like, rather than as a rounded performance. It would be nice to see how she came across in a more intimate venue.

There are faults in the production, too, especially in the slack first half, depicting the Joad family's journey from the Oklahoma dust bowl to the vineyards and orchards of California. Along the way they discover, in a reversal of all the musical cliches, that Oklahoma is far from OK and there are precious few kicks to be had on Route 66.

At stages along their journey, boards are lifted to reveal a real camp-fire, real earth (for burying grandpa), real water (for splashing around in). The impression is that these primary elements are incorporated in Mark Leese's Spartan set for some definite reason; whatever message they are meant to convey is obscure, and these episodes interrupt rather than illuminate the plot.

The second act, when the kindly, simple Joads are jerked into political awareness by the exploitation they meet in California, works far better. Steinbeck's message, about the need for people to act in union - and more specifically, in unions - is allowed to speak for itself, with no overt preaching.

Throughout, though, uneven pacing stifles the play's impact - the final image, of Rose of Sharon, who has just lost her baby, offering her breast to a starving man, should be shocking, but it's denied the dramatic pause it needs. This moment could stand for the whole play: something powerful is hinted at, but never quite happens.