The story of how fey fragile Oscar Hopkins, the son of a fanatical but upright father first embraces Anglicanism then gambling and then, with fumbling mute pathos, Lucinda Leplastrier will live as one of the great Australian stories (if ‘story’ is the word). One of the peculiarities of Peter Carey’s talent which this film does not succeed in disguising is that he is a writer with very formidable narrative gifts who is, at the same time, often incapable of sustaining (or unwilling to sustain) his own narrative logic. He is a magician of narrative momentum or line but then defeats expectation (often with the most cartoonish or comic strip effects) chat can look like copouts.

Why does Mr Stratton, Oscar’s clerical mentor, who has been a comic character for most of the book’s action, commit suicide and why doesn’t the novelist do more with this if he is going to introduce this discordant note? Why are there mad interludes like Oscar’s incarnation as Mr Smudge, the worst of all clerks? Why does Jeffris, the clerk who leads the expedition, turn into a monster of sadism and why does the narrative darken so murkily under his influence? Why indeed does Oscar not simply get his Lucinda and why if there is to be complication and tragedy should this come through the skeletal and improbable offices of Mrs Chadwick?

There are, I think, answers to some of these questions and not to others. But whether you are an unambiguous admirer of Peter Carey or whether, like me, you think he’s always in danger of biting off more than he can chew, that he’s given to shifts of tone and focus that dissipate the coherence of his books, there is no doubt that Oscar and Lucinda generates enormous poignancy from the gap between what happens in the mutating whirligig of the book’s action and how this has significance in the minds of the main characters. And, in this respect, Carey’s magic and his realism are sufficiently contraindicated to make him radically undramatic in any structural sense, Aristotelian or otherwise.

This is almost the alpha and omega of what goes wrong with Gillian Armstrong’s bright and beautiful looking film of Oscar and Lucinda. The two main characters are perfectly cast, the script is reverently transcriptive of the book’s action and dialogue, both the Englishness and the Australianness of Oscar and Lucinda’s ambience (its contrasted idioms and landscapes) are incarnated with tact and skill but neither Gillian Armstrong’s direction nor Laura Jones’ script can provide an equivalent to the écriture of Carey, the strange compelling quality of the aporia he creates, which is all in the gap between the comic buoyancy of the hope the narrative sets up and the crashing caricatured cataclysm which ensues so that Oscar with his goodness and oddness and ineffectuality seems like the objective correlative of a book that burns in the mind even as it sinks like a glass church.

Armstrong is a naturally extroverted director and she has no way into the haunted spaces behind Carey’s farce. We never know as an audience the depth of Oscar’s despair when the sea storm comes like the voice of God to condemn his vice nor – quite crucially – do we get the naïve complexities of Oscar’s love of Lucinda or Lucinda’s love for Oscar.

Laura Jones who wrote such a powerful concentrated script for The Well puts too much faith in the idea that a detailed cinematic quotation of the book will reanimate its power but she is so much of a literalist in following Carey even when his action makes no outer sense that significant parts of the film are opaque to the point where they will bewilder audiences who do not know the book.

Nor does it help that Armstrong who is fine at directing her actors through the script is incapable of finding a language between the words. The upshot is a gorgeous and tasteful flyer for this bejewelled scarecrow of a book. Geoffrey Rush does the narration (a desperately literary strategy) and does it very well. A host of Australian actors – Robert Menzies and Gillian Jones, say, as Lucinda’s parents – play second fiddle, ably enough, to the best of British. Norman Kaye is particularly good as the Sydney archbishop, Dancer, and it’s true that Armstrong is very skilled at generating an expansive and flexible sense of an older ‘Anglo’ Australia where stereotypes bleed into each other and intermix interestingly. Though in this respect Ciaran Hinds, faced with the inarticulateness of his script, is less soaring as Hasset – the man Oscar imagines Lucinda loves – than he might be. Richard Roxburgh, although he is dashing as the sadist Jeffris, seems a little uncertain about how English or how Australian he wants to sound.

No such uncertainty afflicts Ralph Fiennes and Cate Blanchett as Oscar and Lucinda. Armstrong is blessed in her leads. Fiennes captures and cherishes the mysterious goodness and frailty of this Odd Bod in a performance of swooping poignancy and self-effacement which is as fine as anything this actor has ever done and which does Carey proud. Blanchett captures all the cheek and bubbling ornery love in Lucinda with a wonderful precision and grace.

It is dream casting and we should be grateful for it though it is not enough. This thwarted chocolate-box film Oscar and Lucinda, with its two glowing central performances, will stand for a long time as a pointer to a book which it impersonates with great skill but only fitfully penetrates.