THEATRE / Blithe new life for Coward's walking dead: Post-Mortem - King's Head; Trilby and Svengali - Nuffield, Southampton; Dream -Crucible, Sheffield

NEVER ONE to undervalue his own work, Noel Coward came as close as he ever did to self-disparagement in the post-mortem on his unperformed 1930 piece, Post-Mortem. 'I wrote it' he said, 'too hot off the grid': and, as a result, produced something that was 'shallow', lacking in 'real experience', and which 'muddled the issues'.

Learning that these issues involve the 1914-18 War and its aftermath arouses expectation of a stinker. On the strength of having played Stanhope in a Singapore production of Journey's End, how dare Coward enter into competition with Sherriff's masterpiece? Evidently this occurred to him as well; for, despite defensive claims that the play contained some of his best writing, he never risked putting it on stage. He tried the script out on T E Lawrence, but with the reservation that it was for publication only.

Synopsis confirms one's worst fears. John Cavan, son of a newspaper baron, is killed in action and makes a spectral return to London in 1930 to see how the brave new world is getting on. He finds it peopled with heartless pleasure-seekers and moralising hypocrites, all rotten to the core. His former sweetheart has shrivelled into a loveless wife, his old comrades into sclerotic blimps. His father is planning the journalistic slaughter of one of Johnny's brother-officers for his anti-war poems, only to be forestalled by the poet's suicide. His mother laments the passing of the old values. Johnny registers the futility of his generation's sacrifice and recedes forever into the shades.

No need to dwell on the muddle: the unexplained 13-year gap between the hero's death and return; the indiscriminate line-up of actual and fantasy targets; the idea that doltish patriotism and hypocrisy were post-war inventions. You see it all coming, and the story doesn't add up. Except that this is not a story.

In Richard Stirling's well-cast production the piece takes on a vitality that perhaps not even Coward suspected. This does not lie in the indignant tirades, but in the process of shaping hysterical emotion into theatrical fact. He never wrote such a play before or after; and from line to line you can sense it stretching his technique. The dugout prologue, for all its editorialising passages, is capable pastiche Sherriff. But the real achievement comes with the London scenes. In a story, you can simply announce the arrival of a ghost; but how does a ghost behave on stage? Coward's solution is to present the boy as he was at the front, in the same muddy, bullet-riddled uniform. He can drink, sit down, embrace; no one shows the slightest surprise at seeing him again. Nor, apart from his mother (Sylvia Syms), do they take much notice of him.

'Weren't you killed in 1917?' inquires a dinner-suited husband (Ian Michie) pleasantly, finding Johnny in a clinch with his wife. 'Whatever happened to you in death hasn't improved you,' barks an old comrade. The production reflects the play's stylistic inconsistencies by making decisive gear changes from comic realism to expressionist caricature; but always so as to define Harry Burton's puzzled, well- meaning Johnny as a social outsider. To the living, he is simply out of the swim; dead or alive, it is bad form for him to gatecrash the party in those dreadful clothes. The dialogue between the living and the dead generates a more devastating comment on clubland England than any explicit denunciation. The result may not rank as a war play; but, if morale- boosting counts, Coward went on to produce the most successful war play of the century in Blithe Spirit, which brings another revenant on stage. It was in Post- Mortem that he learned how to do it.

Beerbohm Tree built Her Majesty's Theatre on the proceeds of George du Maurier's Trilby, and - judging from David Fielder and Nancy Meckler's touring version, Trilby and Svengali - you can see why: it reconciles archetypal myth with popular melodrama, and launches a vampire outclassing Dracula. Svengali, the down-and-out music teacher who mesmerises his tone-deaf protegee into a bel canto goddess, combines Shylock and the Phantom of the Opera. The meaning of du Maurier's fable exceeds his plot. Svengali loses and destroys Trilby by possessing her. But if she had got it together with her true love Billy - romantic young artist turned stuffy RA - she would also have been destroyed. And her outcast status, as an artist's model, is mirrored by Svengali, who has the key line: 'Always a Jew - they don't see me.'

Meckler's production offers a gorgeously mischievous Trilby (Tilly Blackwood), and exposes the racism of the Latin Quarter Brits without vilifying them. But its chief ornament is Teddy Kempner's astounding Svengali, who has the power to change shape from a ramrod-backed autocrat to a grovelling underdog easily picked up by the scruff of the neck. His voice undergoes extraordinary changes from hammer-tap repartee to whinnies of panic as he coaxes, caresses, enchants and bullies his way from the gutter to the stage of Drury Lane: 'Tzerty-two beautiful British teeth,' he croons appraisingly, mesmerising the audience hardly less than his pupil.

Michael Rudman launches his regime at the Sheffield Crucible with a heavily cut version of A Midsummer Night's Dream which we are invited to see as the dream of Theseus. This allows for wholesale doubling, and for a unitary set (an overgrown marble temple, by Kendra Ullyart); but also leaves you wondering why Bottom and the lovers wake with memories of fairyland if it only exists in the mind of Theseus-Oberon (Michael Mueller). Otherwise the show is full of lovely comic detail. 'What is this Pyramus?' inquires Bottom (Anthony Brown) as though querying an order for textiles. Titania (Alex Kingston) and her followers emerge as a magical reflection of the Athenian court. And the sparring lovers are all the funnier for interrupting the fight to show their wounds. The music (by Matthew Scott) is terrific.