Like the hottest new fashion trend, ?The Devil Wears Prada? is initially irresistible. Fun, flirty, spirited, sexy ? you can?t take your eyes off it. You?ve gotta have it.

And then just as powerfully as it bursts onto the scene and commands your attention, it dies.

Certainly the film from director David Frankel, based on the script from Aline Brosh McKenna, had to be superior to its source material. Anything would have been.

Lauren Weisberger?s best-selling novel of the same name, inspired by her own experiences working as an assistant for Vogue magazine Editor Anna Wintour, was chock full of juicy little details about the fashion world, but it was so coarsely written it was agonising to finish.

(Guess that?s why they call it a beach read. Your mind is elsewhere as you turn the pages ? on whether your shoulders need more sunscreen, on that cute guy a couple towels over, on ordering your next mai tai ? so you?re not really paying attention to the quality of the book in your hands.)

The would-be Wintour figure, editor of the fictional Runway magazine, was too two-dimensional; arbitrarily demanding and cruel, she never showed a glimmer of humanity.

It was impossible to believe the capricious, venomous extent of her actions ? which is a problem, since that?s the basis for the whole book.

Thankfully the film fleshes her out, supplies some much-needed motivation, and Meryl Streep brilliantly brings her to life.

She steals the entire thing away from young Anne Hathaway ? who has the benefit of youth and Patricia Field as her costume designer and who is, theoretically, the star ? and reminds us that, when given the chance, she?s a master of subtle, biting comedy.

And Frankel, having directed episodes of ?Sex and the City? and ?Entourage,? for a long time shows just the right, light touch for this kind of dishy material. But then the film staggers toward its protracted ending, which also deviates from the book, but is needlessly convoluted.

Details differ here and there but the structure of ?Prada? essentially remains the same. Hathaway?s Andy Sachs, fresh out of college and yearning to do Serious Journalism at The New Yorker, instead takes a job as an assistant to Streep?s Miranda Priestly, one of the most powerful figures in the fashion world, with hopes that it will serve as a steppingstone.

Andy?s work consists of the usual menial stuff: dropping off dry cleaning, fetching lattes, arranging her boss? travel.

But Miranda also goes out of her way to torment her underlings: dropping her fur coat and designer purse on Andy?s desk when she walks in the door, sizing up the unfashionable young woman from head to toe, intentionally calling her by the wrong name. (Miranda shouts out ?Emily? ? the name of her other assistant, played with delicious condescension by British actress Emily Blunt ? and whoever answers will suffice.)

Andy gets the hang of it in time, but her unreasonably long hours put a strain on her relationship with her understanding boyfriend (?Entourage? star Adrian Grenier). She?s not afraid to verbally spar with Miranda or her other co-workers ? another welcome change from the book, which depicted Andy as whiny and unassertive ? and the banter gives the film a delightful buoyancy.

And of course, Andy also undergoes the obligatory makeover, a staple of any chick flick or movie based on chick lit.

With the help of Runway?s fashion guru, Nigel (played with unexpected bitchy glee by Stanley Tucci)

Andy learns to cast aside her Banana Republic cable-knit sweaters and tights, and instead opt for a chic array of Chanel, Dolce & Gabbana and Valentino.

Her transformation from preppy to fashionista happens with impossibly dizzying speed. But Hathaway is such a joy to watch ? the ?Princess Diaries? star all grown up ? and she wears the clothes so beautifully, you just sort of shrug and go, ?Why not??

From there, though, ?Prada? gets bogged down in its own machinations, just when it should be building to a climax.

After dazzling us with vivid visuals and dialogue, McKenna drags us through a love triangle involving a hot young writer (Simon Baker) who?s pursuing Andy but is also pursuing an important new gig within Runway, where certain other editors? status hangs in the balance during the fall fashion shows in Paris and ... ugh.

It all gets too complicated and heavy ? a tailored tweed suit when a light chiffon gown would have done just fine, thank you very much.

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