YOU TAKE quite a risk when you cast Joanna Lumley in a once-fashionable 1920s play about a murder in South-East Asia. With this heady combination, it would be all too easy to pick up a laugh with a quaint period expression, a moment of melodrama or a hint of Patsy from Absolutely Fabulous. No such mishaps occur in Neil Bartlett's exemplary production of The Letter. You feel even the author would approve.

Somerset Maugham had been travelling in the Malay Peninsula when he heard the story about a woman who shot a man six times on the verandah of her home. It was just the sort of incident that gave Maugham, a former medical student, material to conduct one of his own autopsies. The challenge for any produc- tion of The Letter is to reveal these flaring emotions with the same diagnostic zeal. Bartlett does just that: steering his excellent cast into a spare, penetrating style that sidesteps melodrama. It's a modest virtue, but a substantial one.

Neil Stacy is particularly moving as the uxorious, optimistic husband. He never patronises his dim-witted character - far rarer than it sounds. Tim Pigott-Smith takes the lawyer, Joyce, from a gravely sceptical position to a tortured, impassioned one. You might not guess, from reading the text, the amount of sexual frustration in the air, but Pigott-Smith seems as tempted by Lumley as his gossipy wife is by the Assistant District Officer.

When playing a 1920s character, Joanna Lumley has the advantage of a naturally plummy accent. She is perfectly at home snapping orders to the servants or making light of serious things. When told that she will be charged with murder, only a certain kind of actress can get away with saying: "I'll just go and change into a jumper." There's no hint of her television persona here. She's brisk, demure and - leaving aside the six bullets she empties into the man on the verandah - impeccably well- mannered. The one irony in her performance is that she is a little more convincing when she is lying than she is when she is telling the truth.

In this engrossing production, the only conspicuous device that Bartlett adds is the doubling-up of the Chinese servants as stagehands. In the scene-changes these actors move props and furniture while grinning and shouting out instructions in Chinese. It's a small shift, but a subtle one, disorientating the audience and making them share something with the colonial characters. It is the feeling that in this environment the servants are the ones who are at home.

Tennessee Williams's first play started life as a story, Portrait of a Girl in Glass, turned into a screenplay called The Gentleman Caller, and finally made it to the stage as The Glass Menagerie. It's hard to imagine it as a film. Strongly auto-biographical, it's an intimate memory play well-suited to a small venue like the Donmar. What better way to launch an appeal for the threatened theatre than with a production of this quality?

The fire escape that leads out of the Wingfields' house in St Louis runs right round the dress circle, creating long, effective entrances and exits, and increasing the family's sense of isolation. In Rob Howell's design, the brick wall and the planked floor are painted blue: a cold, stark backdrop to the dreams that flicker as tentatively as the candlelight.

Sam Mendes directs a top-flight cast with great assurance. Zoe Wanamaker is the mother, Amanda, forever anxious that there will be no gentleman callers for her shy, crippled daughter. Wanamaker makes Amanda a warm, fussy, comical character, bustling round her two children: "Oh, Tom, Tom, Tom, of course I have to make a fuss!" When at the end of an elaborate evening she discovers that the gentleman caller already has a fiancee, she lets out a long "ohhh - how nice" as if someone was slowly letting air out of a tyre.

The two young men are also very good: the ruffled, handsome Ben Chaplin plays the laconic son and narrator, moving from an easy-going wit and charm, to anger and regret, while as the gentleman caller, Mark Dexter makes a remarkably confident and attractive stage debut. But these three performances really fade into the shadows as the evening progresses. It's Claire Skinner as the crippled daughter, Laura, who rivets the attention. A pale, slight, fragile figure, she trembles with nervous suppressed feelings. Lying on the floor she gazes at the only objects more fragile than her - a collection of glass animals. Skinner has an ability to play damaged characters without any suggestion of self-pity. She manages to be urgent and hesitant, fresh and dreamy. Above all she has an exceptional quality of stillness. The only problem with this actress is that she seems so lovely you can't imagine why the fire escape isn't thronging with gentleman callers.

In Robert Delamere's production of Tartuffe at the Manchester Royal Exchange, the first act resembles an early version of a Yellow Pages ad. The dissolute world spread out before us - wine, fruit, cards, masks, candlewax and jazzy music - has to be cleared in a frantic rush when news arrives that Dad is on his way home.

The texture of 17th-century life is rightly given prominence. The resplendent costumes that befit a family acquainted with the King make a dramatic contrast to the hair shirt and dirty bare feet of the religious impostor, Tartuffe. But Delamere can't resist a few extravagant flourishes of his own. There are cacophonous entrances, miners' lamps on servants heads and the King's soldiers flying in on ropes. These are shallow effects when compared with the absorbing power of the arguments. The cast concentrates more on the vigour of the debate than the humour of the situation. This emphasis admirably suits Roger Lloyd Pack's Tartuffe. He's a sallow, serious threat to the household,with a careful incantatory delivery which makes us believe that he has not only conned the master of the house. He has also conned himself.

'The Letter': Lyric, W6 (0181 741 2311), to 14 Oct; 'Glass Menagerie': Donmar, WC2 (0171 369 1732); 'Tartuffe': Manchester Royal Exchange (0161 833 9833).