L.A. cop Bucky Bleichert (Josh Hartnett) gets up close and personal with "Black Dahlia" lookalike Madeleine Linscott (Hilary Swank).

The grisly 1947 murder of a wannabe Hollywood starlet known in death as the Black Dahlia has been Los Angeles' most intriguing mystery ever since.

A bigger mystery, however, is how "The Black Dahlia" manages to make such a mishmash of its Grade-A ingredients.

After all, director Brian De Palma has demonstrated his flair for classy thrills numerous times in movies as different as "The Untouchables" and "Dressed to Kill."

Novelist James Ellroy brought "The Black Dahlia" to the best-seller lists, fictionalizing the murder tale by widening its focus to include two troubled cops investigating her demise.

Cinematographer Vilmos Zsigmond (an Oscar-winner for "Close Encounters of the Third Kind"), production designer Dante Ferretti (an Oscar-winner for "The Aviator") and costume designer Jenny Beavan (an Oscar-winner for "A Room With a View") bring post-World War II Los Angeles to life -- a not inconsiderable feat, considering that most of "The Black Dahlia" was filmed in Bulgaria.

One of "The Black Dahlia's" resident femme fatales, Hilary Swank, has two Oscars, while Aaron Eckhart -- who plays one of the movie's two-fisted cops -- should be up for an Oscar next year on the strength of his scorching performance in "Thank You for Smoking."

Alas, Swank and Eckhart aren't the lead characters. If they were, maybe "The Black Dahlia" wouldn't seem so curiously underpowered.

Yes, there's a definite energy shortage onscreen-- and you can't blame it on Enron. Not with Josh Hartnett and Scarlett Johansson as the leads.

These decorative young players certainly look their roles, decked out in spiffy period costumes and surrounded by clouds of smoke emanating from their omnipresent cigarettes.

Yet when it comes to playing their haunted roles, Hartnett and Johansson prove about as convincing as kids dressed up for a noir-themed Halloween party. Try as they might -- and my, how they try -- they never quite manage to bridge the gap between style and substance.

Which, come to think of it, applies to "The Black Dahlia" as a whole.

Granted, screenwriter Josh Friedman ("War of the Worlds") faced a daunting task in streamlining Ellroy's densely plotted novel. Clearly, something's got to give. Too bad it turns out to be narrative clarity.

Friedman maintains much of the author's rat-a-tat dialogue, but in the cinematic game of show-and-tell, the script too often tells what the movie should show.

As a result, following "The Black Dahlia" sometimes seems as confusing for us as it does for cops Lee Blanchard (wily, live-wire Eckhart) and Bucky Bleichert (a game but terminally bland Hartnett).

Ex-boxers nicknamed "Mr. Fire" and "Mr. Ice," respectively, the poster-boy partners in crime-fighting are on a stakeout that goes horribly wrong -- just as a young woman's mutilated corpse is discovered nearby.

Sliced in half, drained of blood and disemboweled, her head bashed in and her mouth slit into a sinister ear-to-ear smile, the body turns out to be that of Elizabeth "Betty" Short, a 22-year-old whose dreams of stardom (depicted in black-and-white screen test footage featuring Mia Kirshner as the doomed Dahlia) contrast poignantly with her sordid life and ghastly death.

Lee becomes obsessed with the investigation -- much to the chagrin of his girlfriend Kay (Johansson), a blond bombshell who's determined to bury her past for as long as possible, but knows she's on borrowed time.

Bucky, meanwhile, follows the clues to a shadowy nightclub where he encounters Dahlia doppelganger Madeleine Linscott (the alluringly lurid Swank), a high-society seductress whose behavior seems positively unhinged -- until he meets her even more deranged family.

All of this is designed to transport us to a place we've visited many times before: deceptively sun-dappled Southern California, where crime and corruption co-exist with sunny skies and starry-eyed dreamers doomed to disappointment. (The lucky ones, anyway.)

Although Friedman's screenplay often stumbles over its clunky storytelling, De Palma's direction (aided immeasurably by Zsigmond's fluid camerawork) ably reveals the dangerous, ever-shifting ground under the characters' collective feet, emphasizing their duality (and their duplicity) through a variety of vivid visual devices.

True to form, De Palma also delivers more than one of his Hitchcock-inspired set pieces, expertly employing shockingly stylized violence to distract us from the movie's essential mystery.

Then again, there are some mysteries no one can solve. Including, apparently, the one that involves bringing "The Black Dahlia" satisfyingly to the screen.