Dir: Manoel de Oliveira. Portugal 2002. 133mins.

Nowadays more prolific than ever, 93-year-old Portuguese veteran Manoel de Oliveira continues to follow his own wildly idiosyncratic path. Although in many ways decorous, even a little staid in its composure, The Uncertainty Principle is overall a characteristically eccentric venture that is as likely to baffle non-acolytes as it is to dazzle admirers - and chances are it will baffle plenty of those too. Closer in tone to his recent oblique works such as O Convento and Party than to last year's unusually accessible Cannes hit I'm Going Home, The Uncertainty Principle lacks the latter's obvious box-office potential as a modest art-house hit. But Oliveira's festival devotees will be in raptures watching it and then arguing over what it all means.

More ambitious in both size and narrative complexity than his last few films, The Uncertainty Principle is an entangled family saga with philosophical overtones - its story something between an Iris Murdoch novel and an upmarket TV soap. The film begins with two elegant middle-aged brothers, Daniel and Torcato Roper (Luis Miguel Cintra and Jose Manuel Mendes) filling each other in on the story's convoluted list of dramatis personae - a story all the harder to follow because of the characters' bizarre nicknames. The main story concerns two young men - wealthy Antonio, aka 'the Red Carnation' (Ivo Canelas), and Jose Luciano, or Blue Bull (Ricardo Trepa), the disreputable son of domestic servant Celsa (Isabel Ruth). More devoted to the seemingly innocent Antonio than to her own son, Celsa gets the Ropers to use their influence and arrange for Antonio to marry the much-admired Camila (Leonor Baldaque). Her apparent virtue is stressed in comparisons with the Virgin Mary and Joan of Arc, whose cobwebbed statue she secretly prays to.

All, however, is not as it seems. Slyer than she looks, Camila seems intent on settling an amorous score with her admirer Blue Bull. And Antonio proves only too corruptible, falling into the seductive clutches of Blue Bull's lover and business associate, vampish brothel-keeper Vanessa (Oliveira's long-time muse Leonor Silveira, giving a performance of sublimely arch silkiness).

The stakes in this bizarre melodrama prove to be nothing less than metaphysical - especially in a deliriously strange climax when a disco is invaded with a dancing troupe of arsonists wearing devil masks. As he often has, Oliveira bases his script on a novel by Agustina Bessa-Luis, and the film's literary origins show in the densely-written dialogues, in which the characters wax philosophical and enigmatic, debating the nature of good and evil, reality and appearance, corruption and innocence. But Oliveira's sardonic, mischievous wit is unmistakable in some of the bizarre propositions bandied around: "Women are like artichokes", "People who don't have split personalities are what we used to call epic figures."

Renato Berta's stately, static cinematography keeps the viewer at a discreet distance, reinforcing the film's deliberately stiff theatricality. Some interiors seem chosen for maximum fustiness, the dark, cluttered interiors of Antonio's house and the Ropers' flat suggesting the settings of a particularly severe nineteenth-century novel. The film has an usually strong sense of place, its episodes divided by interludes - set to the music of Paganani - in which the camera gazes at length out of the window of a train shuttling back and forth along the River Douro.

Typically for Oliveira, there's nothing naturalistic about the acting styles, either; getting up from a bed to greet Vanessa, Camila executes an elaborate roll into the sitting position before bursting out into mad laughter. Unusually for the director, however, there is a strong erotic undertow, both in the verbal fencing and in shots such as a deceptively chaste close-up of Antonio's hand on Vanessa's knee.

For many viewers, The Uncertainty Principle will be a tiresome conundrum, while even Oliveira fans may find their patience tested by the prolixity of much of the dialogue. But there's plenty to relish here, including Leonor Baldaque's lead as the deceptive ingenue Camila, at once sly and self-contained. And it's hard not to enjoy the way that Oliveira, always seems to be enjoying a private joke at our expense. Visually and verbally, there's a definite music to this elegant shaggy dog story. When one character says, "You don't need to understand, just listen," it just about sums the film up.

Prod co: Madragoa Filmes
Fr dist: Gemini Films
Int'l sales: Gemini Films
Prod: Paulo Branco
Scr: de Oliveira, adapted from the novel 'Joia de Familia' by Agustina Bessa-Luis
Cinematography: Renato Berta
Ed: de Oliveira, Catherine Krassovsky
Prod des: Maria Jose Branco
Music: Nicolo Paganini
Main cast: Leonor Baldaque, Leonor Silveira, Ricardo Trepa, Ivo Canelas, Isabel Ruth, Luis Miguel Cintra, Jose Manuel Mendes