At times Brian De Palma shows signs of the genius some attribute to him. Deep into The Black Dahlia, his adaptation of the James Ellroy novel, a crane shot starts with the two protagonists, LAPD officer Dwight “Bucky” Bleichert (Josh Hartnett) and Sergeant Lee Blanchard (Aaron Eckhart), at a stakeout. The camera wanders down the street, following a couple in conversation who are walking to the place the cops are watching. Then it sails over their heads and over a building and glimpses in long shot a vacant lot and a screaming women running from a discovery. It’s the body of Elizabeth Short (Mia Kirshner), sliced in half at the waist, eviscerated, a hideous grin carved on her face from ear to ear. She will become known as the Black Dahlia.

This unobtrusive and discreet — the carnage is not shown, a rarity for De Palma — camera movement compresses at least three story lines and scores of pages of the original text into one elegant gesture. That’s one of the challenges of adapting Ellroy: finding the story line in the midst of churning subplots, digressions, and obsessions. Curtis Hansen did so masterfully in L.A. Confidential (2003). To his credit, De Palma maintains a pulpy clarity pretty much up to the scene described above. But once the body turns up, the film turns into, well, a De Palma movie, with its narrative absurdities, its stylistic excesses, its hammy acting, and your uneasy sense that the whole thing might be a big joke.

In retrospect, you can see how early signs point to this outcome. The casting, for example. As Bleichert, a young cop resourceful and disillusioned beyond his years, Hartnett comes off as squeaky and callow, his first-person narration no match for Ellroy’s brawny prose. As his partner, the volatile veteran Blanchard, Eckhart seems glib and inconsequential. The two take their professional partnership into their personal lives, indulging in a tentative ménage with the damaged and enigmatic Kay, who’s played by Scarlett Johansson in a performance that convinces me she’s the most overrated and annoying actress on the screen today.

And then there’s the Dahlia herself, present only in ghostly black-and-white “screen tests,” with De Palma’s voice off screen creepily calling out directions and prying into her inadequacies, dreams, and delusions. But then the dead girl gives everyone, not just De Palma, the excuse to go off the deep end. Blanchard becomes obsessed with finding the killer for a variety of motives, not all of them immediately disclosed. Bleichert worries about his friend, but he himself starts taking up with rich girl Madeleine Winscott (Hilary Swank), a material witness who likes to dress up to look like the Dahlia. (Swank doesn’t resemble Kirshner, who doesn’t resemble Short.) Pretty kinky, but the worst is yet to come, as the exquisite corpse leads all into a kaleidoscope of treachery, madness, and evil . . .

What comes off as hard-boiled (despite its extravagance) in Ellroy is only half-baked with De Palma. Things take an especially wacky turn when Fiona Shaw as Madeleine’s mother flips out in a mad scene that combines the best of Nosferatu and Norma Desmond. And no De Palma film would be complete without a Rube Goldberg–like “tour-de-force” sequence, or most depressing, a climax disclosing his abject misogyny.