FILM / Recipe for trouble: Adam Mars-Jones on David Hare's The Secret Rapture, the cinematic equivalent of a pressure cooker with the lid off

There is nothing in the theatre as inherently powerful as a close-up or a zoom, and yet film is, in Marshall McLuhan's not altogether discredited terminology, much the cooler medium. The simple fact that cast and audience in the theatre share a finite space for a set duration allows each dramatic situation to release its juices over time, while film paradoxically suffers from its huge range of choices, the constant reflexive change of context and point of view. Anyone who adapts a theatrical success for the screen, as the writer David Hare and the first-time film director Howard Davies (who directed the original stage production) have been bold enough to do with The Secret Rapture, is like a cookery columnist trying to adapt a pressure- cooker recipe for the microwave. The effect of the 'opening out' that drama requires - the necessity for more detail, if nothing else, the spelling out of what is implicit - is usually that of a pressure cooker which someone has unaccountably forgotten to put the lid on.

In the theatre, the changes that afect two very different sisters when their father dies and his much younger lover is unleashed into their lives, may have carried conviction. On screen, the rollercoaster rate of power reversal and the sheer abruptness of the characters' U-turn give the melodrama a foreshortened quality that is unintentionally comic. Katherine (Joanne Whalley-Kilmer) is an alcoholic in intermittent recovery whose every dysfunctional instinct is for guilt-tripping and blackmail, and who is somehow allowed to rampage unopposed through more organised lives. Isobel (Juliet Stevenson) is a strong and loving person who can nevertheless be manipulated by anyone who presses the button marked Father. Marion (Penelope Wilton) is a high-flying politician with an inferiority complex the size of a tower block about her younger sister.

This doesn't seem a very satisfying role for Wilton, who re-reates her stage interpretation. Marion announces the keynote of her character in almost her first speech: 'You always make me feel I'm in the wrong,' and spends the rest of the film elaborating on it, usually by reacting angrily to accusations that haven't been made. But there is considerable fascination in watching Whalley-Kilmer and Stevenson share the screen.

Since Scandal, Joanne Whalley- Kilmer has specialised in roles of sexual manipulation. She has Americanised her persona to an extent that makes her earlier television work (Edge of Darkness, The Singing Detective) seem like a different performer's. Juliet Stevenson by contrast has retained a sort of radiant reserve. Whereas Whalley-Kilmer's screen presence is hyper- sexualised, Stevenson's retains the possibility of genuine eroticism. She can express sexual intensity precisely because she hasn't allowed herself to be marketed as any sort of sex-pot. Both actresses have low throaty voices, but where Whalley-Kilmer turns every sentence into a proposition, Stevenson's voice remains an instrument of great variety and power.

Stevenson certainly carries The Secret Rapture to the limited extent that it is portable. When the camera first shows her, Isobel is weeping convulsively and nakedly embracing what we are slow to realise is the dead body of her father. Stevenson may yet fall foul of the Gazza factor, and find that even tears are subject to the law of diminishing returns, but for now she is the supreme screen crier. It helps that she can combine rawness and grace so powerfully, and can convey with her voice that the character finds her own pain ugly. She definitively shuts off the possibility that we will think Isobel is wallowing, and she can give a sigh the force of a suicide note.

Isobel is the central character of the story, but in writing the screenplay David Hare could have done more to make her point of view continuous. At one stage, with her life in turmoil, Isobel simply disappears from her world, which is irritating as well as mysterious. If the camera can follow her into the privacy of a shower or bed, why not into whatever solitude she is seeking? And if the script can't be bothered to establish a plausible context for the heroine's actions, how can we be expected to follow her imaginatively? It doesn't help that she reappears with a little falter of stagy exposition: 'When I rang I asked both of you to come here . . .'

Hare's language isn't unduly concentrated or poetic for the theatre, but on screen it cries out for naturalistic dilution to disguise its purposefulness - the way characters expose their conflict with no loss of time. Howard Davies as director faces an equivalent problem, of giving the cinematic impression of narrative prose, and of coming up with a range of detailed backgrounds and objects, only some of which are crucial props. You need a lot of roman type on the page, if your italics aren't going to look silly and overdone.

Nothing in the film, though, manages to be neutral. Every item of clothing that Katherine wears sends a message: the fish-net stockings she thinks appropriate for her lover's wake, the tarty pin- stripes, push-up bras and feather boas she imagines to be suitable as business dress. No one, not just the alcoholic, is allowed an uneditorialised relationship with a bottle or can. When Isobel's lover Patrick (Neil Pearson) helps himself to a beer before a business meeting, it unmistakably signals the onset of the yuppie breakdown that will soon have him forgetting to shave and neglecting his Alessi kettle.

Richard Hartley's music establishes a mood of elevated sombreness at the opening of the film - a trumpet sadly soaring as Isobel in her beleaguered integrity sadly soars - and is used too much thereafter to underline what is already not exactly subtle. Ominous music announces but does not make convincing the regular outbreaks of violence or self-destructive behaviour. The supreme episode in this line is one where Katherine is goaded into taking a drink by a group of leering businessmen (a fish-eye lens helps us to notice their impure intentions) who she fondly imagines are going to give her their business.

Soon she is clutching a tumbler of spirit the size of a small gasometer. When the businessmen let the mask drop and openly jeer at Katherine's tartiness, and the loss of control they have encouraged, she responds with a steak knife in a sequence worthy of a horror film spoof, or to be more charitable, Polanski's The Tenant, where it was at least possible that laughter was a licensed reaction.

(Photograph omitted)