The Quivering: A Matter of Life and Death, devised by the cast and director. Directed by Nikki Heywood, dramaturgy by Virginia Baxter, set design by John Levery, video by Suzon Fuks, lighting design Andrew Meadows, sound design by Brett Collery. With Dawn Albinger, Scotia Monkivitch and Julie Robson. SacredCOW @ La Mama Courthouse until July 22.

Robert Frost famously denounced the writing of free verse as being like "playing tennis with the net down". But, as any fule no, it's actually very difficult to write free verse. To keep the poetic line from slackening into what harrumphers denounce as "chopped-up prose" requires considerable metrical and intellectual inventiveness: you need an acute ear for rhythmic variation as well as a solid sense of linguistic drama. This is why Ezra Pound is a genius, despite his shonky political views, and Patrick McCauley isn't.

The same factors apply to theatre that eschews narrative. Without the formal convention of a plot-line to carry them over longueurs, devisors have to work very hard to keep an audience interested. (And sometimes, no matter how hard they work, individual audients are not prepared to go there - but that's another issue). What this kind of theatre permits - as in, for example, the extraordinary theatre of Romeo Castellucci - is an unmediated intensity, untamed by the closures that narrative often (but not always) provides. It demands accuracy, intellectual suppleness, intense commitment and, most of all, the quality that Peter Brook claims is the root of all theatre, contrast.

One of the risks of dropping conventions in order to invent one's own is - strangely enough - cliche. If the subtext that is thereby lifted to the surface (rather than basking beneath the ripples of story) is too simplistic, the result can seem all too obvious. And The Quivering - a meditation on the moment of death devised and performed by Brisbane company SacredCOW - falls right into this trap. It has a few extraordinary moments: the heart quickens, the eye is delighted, the skin is goosebumped. But sadly, these moments emerge like plums in a bowl of cold porridge.

The Quivering rewrites the myth of the Sirens, the beautiful women who lured sailors to their deaths in the Odyssey. Here they become guides through the moment of dying, the transition between life and death, and absorb the traditional women's tasks of laying out and lamenting the dead. The Sirens - who, being three, also evoke the Fates and the Muses - are imagined as three waitresses in an outback roadhouse, Maureen (Julie Robson), Sharelle (Dawn Albinger) and Singrid (Scotia Monkivitch), who play cards, take orders and, well, wait, in between enacting the process of death.

The show is structured in 16 parts, which allows me to work out that I liked exactly a quarter of it. I thought four parts - the circular beginning and ending,"Monster and Illusions" and "The Fall: Part 2" - were simply astonishing: here the performances sparked alive and the theatre reached into the truly mythic, integrating its various elements to create spectacular stage imagery. A large part of their beauty comes from Suzon Fuks' video projections, abstracted ripples of light and water or billowing flames, which play over the performers, making them seem like elemental spirits rather than human bodies.

Most of all, these moments were unexpected, creating the "perpetual slight surprise" that is as important in theatre as it is in poetry. This was not the case in so much of this show, where I knew too often not only what movements were going to come next, but what words. (If I can do this, gentle reader, something is wrong - I'm bad at second-guessing plots in generic Hollwyood movies).

One problem is the performances, which, apart from Monkivitch, err on the side of caricature. Monkivitch maintains a physical and emotional accuracy throughout the show that at moments makes her riveting to watch, but the other performances often seemed blurred to me; they came across as well-meaning generalisations that, given the gestation of this show (it was first conceived in 2000) should have been polished to gleaming specifics.

But the main problems exist in the orchestration; that is, in Virginia Baxter's dramaturgy and Nikki Heywood's direction. There was far too much second-guessing the audience ("I know this isn't what you expect"), which is patronising, rather than challenging; and the direct address to the audience most often seemed ill-conceived, or even naff. But really, the deepest problem was in its use of repetition. Repetition either deadens or intensifies: the pleasure of repetitive intensification, as Bach knew well, is in its unexpected and subtle variants. But the repetition in The Quivering serves only to circle around an initial idea, neither expanding nor contradicting it.

The effect is to make the show's message - that if we are to be properly alive, we must first understand our own mortality - platitudinous, rather than profound. It's a shame, because its peak moments demonstrate what The Quivering could have been. As Nietszche said in his roundhouse condemnation of poets: "they have not thought deeply enough: therefore their feeling - has not plumbed the depths".