Adaptation is a brilliant exercise in complicated simplicity. At heart, the concept couldn't be much more elegant. Charlie, the critically feted screenwriter of Being John Malkovich, has been approached by Random House to adapt The Orchid Thief, a book by The New Yorker staff writer Susan Orleans (Meryl Streep). He's impressed by the way her conversations with passionate redneck John Laroche (Chris Cooper), a cagey fellow who's co-opted some Seminole Indians to help him get his hands on some rare endangered orchids that grow in the Florida swamps, revealed a void in her own soul, a desire to discover some passion of her own. But he can't figure out how to adapt the book into a screenplay.

The scenes showing Charlie growing more and more manic as he tries first to shoehorn cosmic themes into the story - it's about Darwin! Evolution! Biology! The murk at the beginning of the world! - and finally, desperately, writes himself into the script, are crazy with excitement. Adaptation is surely one of the great movies that endeavors to depict the grand frustrations and the little triumphs that inform the act of writing. Conceptually, it's equally dazzling. Kaufman-the-screenwriter pulls off the incredibly neat trick of making the film seem like it's writing itself as it goes along, with Charlie's various epiphanies (and sexual fantasies) informing the style and content of what we see on the screen. His diametric opposition to the aesthetics embraced by Donald, who's banging out a screenplay replete with gimmicky hooks and textbook symbolism, gives the film an eloquent critical voice (one that eventually turns all too self-aware, but I'll get to that in the last two paragraphs).

Moreover, both Cage and Cooper give what may well be career-best performances. Chris Cooper in particular has been cast in so many utterly square roles (the haunted sheriff in Lone Star, the latent-homosexual dad in American Beauty) that I wouldn't have guessed what a phenomenal job he would do in the role of the life-damaged borderline nutjob he plays here. Meryl Streep is fine but, hey, you kind of expect that. Director Spike Jonze presides over all this with the kind of light touch that ensures you barely notice he's there, but he gives the film a compelling, almost musical rhythm - particularly in the scenes where Cage essentially talks to himself, which are deftly choreographed and 99 percent convincing. What caught me off guard were the film's more reflective moments, which are occasionally very beautiful (and benefit greatly from a voiceover that quotes liberally from The Orchid Thief itself).

Jonze holds this all together for the film's first two acts, but then it gets messy. The problem is that Adaptation finally paints itself into a corner. Once Charlie takes the grand exhortations of screenwriting guru Robert McKee (played here by a galvanizing Brian Cox) to heart - after the voiceover vanishes from the soundtrack and Charlie calls his hack brother to help him fabricate a third act replete with conflict and closure - the movie stops using Charlie to comment out loud on formula Hollywood screenwriting and instead engages with it formally through outright mimicry. That's a problem, since Kaufman and Jonze aren't good enough at counterfeiting the typical B-grade thriller to convince me that they have anything meaningful to say about it.

So if the final act, which features an action set piece and a dialogue scene in which the two Kaufmans share a special moment together, is meant as an endorsement of compromise (of adaptation, if you will), it's a strangely unconvincing one. And if it's meant as straight-up parody, then Jonze and Kaufman really blew it. If Jonze had mustered here just one tenth of the mad energy that went into creating, say, his music video for the Beastie Boys' "Sabotage," Adaptation could have careened through a riotous, ironic climax. Instead, the final third of the film is conceptually rigorous but dramatically inert, discarding supporting characters that we've come to care about in the pursuit of a more abstract agenda. This stuff may be funny in theory, but the film is so rigorously intellectual that it steps all over its own punchline. And the more serious Jonze and Kaufman are about the life lessons that their film purports to impart, the more self-satisfied and, yes, condescending, Adaptation starts to seem. It's a miscalculation that has the unfortunate effect of deflating the grand accomplishment that Adaptation comes tantalizingly close to being.