To sink or to swim: that is the question. In "Little Fish," Cate Blanchett does both. The great Australian actress sinks into the role Tracy Heart, a 32-year-old recovering drug addict who manages a video store in Cabramatta, a Sydney suburb nicknamed Little Saigon for its large Vietnamese population and known as the heroin capital of Australia. As in all her screen performances, Ms. Blanchett immerses herself completely in her character, a damaged, high-strung woman determined to live the straight life while surrounded by temptation.

Recurrent scenes that push the sink-or-swim metaphor too insistently show Tracy doing laps in a pool, treading water and dunking and bobbing to the surface, anxious, watchful, impatient to get on with her life. Will she stay off drugs? To its credit, the thorny, compelling drama, directed by Rowan Woods from a screenplay by Jacquelin Perske, is more concerned with examining the conflicted, complicated relationships among its characters than with exploiting the will-she-or-won't-she aspect of Tracy's perilous situation.

If "Little Fish" is considerably more upbeat than Mr. Woods's last film, "The Boys," a harrowing study of a man's return from prison to a nightmarish family of surly deadbeats, its view of the world is still unsentimental, bordering on acrid. And the film's bleached-out color reflects its parched emotional atmosphere. The hyperrealistic screenplay sketches Tracy's family relationships in an elliptical style that pointedly omits neat explanations in underlined sentences; you have to read between the lines.

Tracy's road to self-fulfillment is paved with setbacks. Because of her record of credit-card fraud during her druggie days, her applications for a bank loan to buy and expand the video store are bluntly rejected. And although four years have passed since Tracy went clean, she is surrounded by physical and emotional wreckage from the bad old days.

Four years earlier, Tracy's brother Ray (Martin Henderson) lost part of a leg in a car crash in a vehicle driven by her ex-boyfriend Jonny Nguyen (Dustin Nguyen), a slick, seductive dealer and user who returns from a four-year exile in Vancouver claiming to have cleaned up his act and landed a job as a stockbroker for a Sydney bank. Emotional alarms go off when he drops in on Tracy, who lives with her fiercely protective single mother, Janelle (Noni Hazlehurst). But the old romantic spark between them reignites, and against her better judgment Tracy sleeps with Jonny.

Tracy also refuses to break her ties to Lionel Dawson (Hugo Weaving), a former Australian football star and family friend who introduced her to heroin and who is still using. Lionel, the gay ex-lover of the local drug kingpin, Brad Thompson (Sam Neill), supports his habit by selling sports memorabilia out of his crummy little house. But he is thrown into panic by Brad's brusque announcement of his retirement from the drug business.

If Mr. Neill's cold, efficient drug lord is diametrically opposed to the cliché movie image of a strutting, bling-flashing sadist, the character's dead-eyed indifference to anything but business is just as sinister in its understated way.

Turned away by Brad, Lionel attempts to go cold turkey but breaks down and pleads with Tracy to score some heroin. She reluctantly agrees, making the connection at the train station, where for a scary moment she considers using again.

In his portrayal of a burnt-out athlete on the skids who summons the remnants of his charm to go after what he wants, Mr. Weaving doesn't shy away from embodying a man wallowing in shame and self-degradation. Near the end, "Little Fish" becomes a melodrama involving Brad and his slippery assistant, Steven Moss (Joel Tobeck), who has stolen enough money from his boss to move with his wife into a flashy suburban house. Appended to the movie, this ugly little story culminates in a bloody midnight showdown at a speed factory. If it doesn't quite belong with the rest of the film, it helps tie up some loose plot ends. It also reinforces the movie's dry-eyed assessment of heroin and its stranglehold on people who stay in its vicinity, even after they've stopped using.

"Little Fish" is rated R (Under 17 requires accompanying parent or adult guardian). It has sexual situations, mild violence and scenes of drug taking.

Little Fish

Opens today in Manhattan.

Directed by Rowan Woods; written by Jacquelin Perske; director of photography, Danny Ruhlmann; edited by Alexandre De Franceschi and John Scott; music by Nathan Larson; production designer, Luigi Pittorino; produced by Vincent Sheehan, Liz Watts and Richard Keddie; released by First Look Studios. At the Village East, Second Avenue at 12th Street, East Village. Running time: 114 minutes.

WITH: Cate Blanchett (Tracy Heart), Sam Neill (Brad Thompson), Hugo Weaving (Lionel Dawson), Martin Henderson (Ray Heart), Noni Hazlehurst (Janelle Heart) and Dustin Nguyen (Jonny Nguyen).