Black Swan is a dizzying and disturbing exercise in art-house horror, but despite some great performances it can't quite hold itself together. It's a film that's lost in wild directorial pirouettes, visceral detail and nightmarish imagery.

It may be director Darren Aronofsky's most disturbing film yet, but it's definitely not his strongest, despite the best efforts of his prima ballerina.

After a celebrated realistic hiatus with The Wrestler (2008), Aronofsky is back to surrealism. In his latest offering, he examines the psychological underbelly of New York's highly competitive ballet world and the young women who suffer within it.

 Aronofsky makes the ballet world seem like some evil conspiracy against its delicate ballerinas. It's a world that rewards dedication with eating disorders, injury, early retirement and, in this case, major league mental problems.

The plot has ballerina Nina Sayers (Natalie Portman) landing the role of a lifetime, playing both the White Swan and her evil sister the Black Swan in a remount of Swan Lake. With a domineering mother at home (Barbara Hershey) and a lecherous director (Vincent Cassel) at work, Nina starts to let her dual roles drive her into schizophrenia and implied self-harm. As her obsession and paranoia take over, she begins to suspect that her sexy understudy (Mila Kunis) is out to either seduce or destroy her.

 Oh, and then there's the issue of this weird rash . . .

 The saving grace of the mostly convoluted plot is that nearly every moment focuses on the incredible performance of Natalie Portman. Her character is a driven but mentally fragile dancer whose perfectionism cripples her. This definitely is not the cutesy Portman of Garden State.

What makes Black Swan work is that it takes such a well-known actress and so thoroughly disguises her in her split personalities. In this film, Portman almost literally does the work of three roles, each of them caught in the same deteriorating body. The plot follows the deterioration of a mind as well, but getting lost in Nina's delusions is both fascinating and exhausting.

After about the midway point it's wise to stop trying to follow the literal story and start accepting the allegory. Every scene is so cluttered with symbolism that following the literal plot is a lost cause. It's a nightmare you have to accept in order to wake up.

The images yo-yo between beautiful and repulsive, but never stray from the arty black, white and occasionally red color palate. If this is a modern fairytale then it's the grimmest of the Brothers Grimm.

This insistence on constant and sometimes obvious symbolism is key to why Black Swan is both so brilliant and so annoying. The movie is not so much a story as it is a crazy extended metaphor about sex, control, inhibition and performance. Black Swan is somehow both convoluted and simple. As a depiction of a split personality, it's actually straightforward, but it will try to creep the moviegoer out from every possible angle.

Wandering darkly through the metaphorical and one hallucination scene after another, it's easy to get tired of Aronofsky's characteristic approach. There's a sense that he's trying too hard to continue the successes he had with other hallucinatory films such as Requiem for a Dream (2000).

Black Swan refines but does not clarify storytelling techniques he has had since his first film, the equally intense Pi, another New York-centric movie of destructive obsessions and conspiring, unseen forces.

Black Swan's convoluted nature makes it all the more miraculous that Portman is able to hold it all together. She has some help from some other strong performances such as Cassel's brilliant but sexually abusive director, and Winona Ryder's cameo as an unhinged has-been that Nina has cruelly replaced.

Though Mila Kunis is also great as the sultry understudy, the weight of the film truly rests on the overworked and under-fed Portman. Ambitious, repressed and terrified, Nina the ballerina is one seriously disturbed little bird.

Black Swan is now playing at Landmark Renaissance Place Cinema.