Stratford's main house productions this year have been very patchy. But Trevor Nunn's production of All's Well That Ends Well, strikes me even in the breathless rush induced by a late curtain, as an incipient masterpiece. It takes a dark difficult play and turns it into that rarest of things: a realistic fairy tale.

Very like Guthrie in his ecstatic 1959 version (which I never thought to see bettered) Nunn distinguishes clearly between the play's separate worlds. The Countess of Rossillion (Peggy Ashcroft playing with a wealth of humorous silver-haired compassion) occupies a Chekhovian world of wicker chairs, towering fern and chiming clocks. The fistula-stricken French King inhabits a Novello court packed with peacock captains who vault, fence, dance, and sport like Ruritanian princes. And when the action moves to the Florentine wars we are in a world of brass bands, smoke filled estaminets and peachy nurses who might have stepped out of Oh What A Lovely War!

But although the action—framed by John Gunter's pillared Victorian conservatory set—floats anachronistically between several periods and worlds, it has in this production a binding emotional reality. Thus Harriet Walter's tender Helena is not a ruthless Shavian go-getter but a love stricken medico's daughter, seemingly always on the verge of tears and bursting with passion.

At first there is a teasing playfulness about her selection of Bertram as a husband through the process of an elimination dance at court. But Nunn turns this to naked anguish when Mike Gwilym's ferocious Bertram spits out, "I can't love her" with Strindbergian intensity. You feel she can't help loving this utterly worthless man; and the end acquires a bitter irony as tentatively holding hands, they fade into dusk and the pain of an unequal relationship.

What is impressive, however, is the way Nunn throughout keeps the balance between comic hoopla and emotional pain. Stephen Moore's Parolles is, for example, a splendidly conceived braggart dandy decorated in white scarves like a walking Christmas tree. Yet the famous scene when he is literally hoodwinked and exposed is both funny and uneasy.

We laugh as a fork is scraped against a silver salver to produce the sound of torture instruments. Yet when he describes Bertram as "a foolish, idle boy but very ruttish" we realise he speaks the blunt truth. And the realism of his interrogation even down to the proffered cigarette and glass of water, has something of the cruelty of the dulling of Malvolio.

What Nunn has done is to reconcile the diverse elements of a "mingled yarn" of a play. There is something wholly modern about Helena's reckless pursuit of a man who is an unredeemed monster. Yet when in the elegiac final scene the conservatory doors are flung wide open and she returns apparently from the dead to claim her man, we also seem to be in the realm of some twilit fairy tale. This is pure theatrical alchemy and it is achieved by putting real, suffering people into an unreal situation.

It is also the result of some very good acting to which I would add the names of John Franklyn Robbins, as a tetchy monarch transformed from chairbound invalid to epauletted dancer and of Robert Eddison, who surrounds Lord Lafew with an aura of benign wisdom. By the end you have been taken into a world of magic; but one in which the lovers live painfully ever after.