Who to blame for the stylish mess that is The Black Dahlia? Brian De Palma seems the likeliest candidate, as every frame drips with his stylistic tics and quirks, and it's obvious that he's not really interested in telling any sort of "story." Or perhaps Josh Friedman, whose adaptation of James Ellroy's book retains unwieldy chunks of expositional prose while making an unrecognizable hash of the denouement. Or the actors, who range from mis-cast (Hilary Swank) to simply bad (Scarlett Johansson).

Mostly, I want to accuse Josh Harnett.

Hartnett plays Dwight "Bucky" Bleichert, a Los Angeles cop in the 1940s whose partner ropes him into investigating the grisly murder of Elizabeth Short, the "Black Dahlia", an aspiring actress found bisected and disembowled with her mouth slit from ear to ear. My fear that he would be unable to rise to the demands of this kind of gritty film noir was tempered by my expectation that this would be an ensemble piece in the fashion of L.A. Confidential, but this hope was misplaced: Hartnett is in nearly every scene, and for most of the remainder, we hear him intoning the painfully excessive narration. I had always realised that Hartnett, with his coal-black eyes and synthetic flesh, was unpleasant to look at; never before did I recognise how unpleasant he sounds.

My personal revulsion at the man might be overcome if he were capable of doing anything as an actor, but he cannot, and I understood for the first time watching The Black Dahlia why: he tries very hard. He stands before you on the screen, and the events of the script call for him to be e.g. "sad," and right before your eyes he goes step-by-step through the process of being sad. He scrunches his eyes. His voice quavers. He looks away. He scrunches his eyes harder. He does all of these things one at a time, and the effect is akin to watching Data from Star Trek: The Next Generation attempt to mimic human emotions he does not understand. In a way it's thrilling to see the process of acting laid so nakedly, but Hartnett does not act in experimental films, he acts in narratives, and when the narrative rests so utterly on his shoulders as it does here, all of the things that we tradtionally seek in narrative cinema, like characters and emotions, are completely absent. One pangs to imagine what a great director of bad actors like Stanley Kubrick could have done with Hartnett.

Brian De Palma is not a director of bad actors, and he is not even a bad director of actors, but you would not know that from this film, in which four main characters appear to be residing in four separate films. Of course, the film that Hartnett acts in a student film made by college freshmen who cast their friend who took an acting class back in high school. Scarlett Johansson plays Kay Lake, his love interest and his partner's girlfriend, and she is atrocious - never have I seen her so miserably reduced to merely reciting lines of dialogue and occasional moving her mouth up or down to signify an emotion that was apparently written in the screenplay directions. It's doubtful that either of them could generate chemistry with anyone, but there is most definitely nothing between them when they're together. This is deadly for a film that pivots on our investment in their relationship, which was supposed to be about their tentative attraction running aground of Hartnett's obsession with the murder case.

Aaron Eckhart plays Bleichert's partner, and it seems largely that he's just thrilled to be wearing vintage-style costumes and running around on period sets. His performance is all about energy and fun, and this too is bad: he is supposed to be consumed by the Black Dahlia, but he's much more joyful than tormented. And if I had to date an inflectionless block of wood like Johansson, I'd be happy to study a disembowled corpse, too. Hilary Swank rounds out the main cast and gives the film's only good lead performance as Madeleine, the femme fatale and a daughter of society with a strange connection to Betty Short. Sadly, however good her performance is, both she and the character seem to have stepped intact out of a Tennessee Williams play. This feeling is cemented by Fiona Shaw as her deranged mother, who in two scenes provides a Southern Gothic harpy that redefines the very concept of hamminess, and ends up so absurd and hilarious that I almost want to believe it makes the entire film a parody.

It's not an impossible idea. De Palma is famously delighted with subverting the audience's expectations, and while it may seem strange to make the vicious murder of a young woman the stuff of comedy, he's just enough fixated on the degradations committed against women that I can seem him doing it. Certainly, he doesn't take the story seriously at all, which perhaps explains why the last twenty minutes spins totally out of control, wrapping up too many threads too quickly, in the most arbitrary way. I was reminded of the climax to the crime parody A Shot in the Dark: "They were all murderers, except for Maurice, who was a blackmailer." No, De Palma prefers to focus his energies on his wandering voyeuristic camera, and here's where I start to say nice things.

De Palma, for all that he is an awful storyteller, is a great stylist, and as a purely visual experience, The Black Dahlia is brilliant. Indeed, the epic crane shot that first reveals Short's body in a field, merely one element of a wide canvas of cars and buildings and people, will likely remain as one of the most arresting images I see in a theater this year. De Palma is one of the few directors who can use slow-motion well, and his depiction of violence is rightfully praised, if disturbingly free from moral judgment. His style doesn't mean anything at all, in the end, but it's pure cinema, in love with its own filmic-ness; the heir to the French nouvelle vague in appearance if not in effect.

He's got some big guns helping him, chiefly among them production designer Dante Ferretti and cinematographer Vilmos Zsigmond, both of them among the undisputed masters of their craft. Both are in fine flower here: for Ferretti's part the film captures the look of the 1940's in a rare and wonderful way. It all looks stagebound, but it looks bound to a set in post-war Hollywood, not the 21st century. Zsigmond's cinematography is shockingly non-noir - shadows exist, but they are hardly omnipresent - but it's impossibly lovely, with just the right amount of desaturation. Again, it doesn't add up to anything, but it looks. So. Nice.

"Looks so nice" would be the end of discussing the film, except for one true surprise, and that is Mia Kirshner as Betty Short. She is dead (and a prop) when we first see her, but in the course of investigating, Hartnett finds a film reel containing her audition tapes. Betty Short is a terrible actress and a bad liar, but Kirshner, in a few short scenes, emdbodies her completely and gives the film a human core that none of the other actors come even close to providing. She is not innocent, but she is totally naïve, and the film comes perilously near to meaning something when she is onscreen: the corruption and destruction of something sweet and lovely. It's her eyes, really; Kirshner has the most piercing clear eyes I can remember seeing, and even in black and white it is impossible to look away. They are sad eyes, full of a grim past and an unpromising future. The great films noirs are tragic: they are the stories of the good and the pure dying in the face of the seedy and indecent. The Black Dahlia does not aspire to tragedy, but Betty Short, in those few moments, is good and pure, and in these scenes her death takes on a horrifiying aspect that De Palma seems unwilling to invest it with otherwise. Whatever is true of the morally empty film that contains her, Betty Short is a tragic heroine.