Heavenly Creatures, the latest film from New Zealand writer/director Peter Jackson, appears at first to be an attempt to make that world understandable. What would it take to turn the playful imaginings of two adolescents into the seeds of murder? The story faithfully recounts the budding friendship of Pauline Parker (Melanie Lynskey), a moody, self-effacing schoolgirl, with Juliet Hulme (Kate Winslet), an outspoken and slightly bizarre transfer student from England. The two personalities are complementary, and Pauline and Juliet are soon spending all their time together dabbling in role-playing games, collecting celebrity scrapbooks and listening to "the world's greatest tenor," Mario Lanza.

People can be extremely insular at that age, and it isn't long before they've created an elaborate, ritualistic belief system revolving around the idea of The Fourth World, "a paradise of music, art and pure enjoyment" to which only the best and brightest are privy. In their exclusionary narcissism, the girls decide they hold the key to The Fourth World, and lament "how sad it is for others that they cannot appreciate our genius." When illness or family conflicts threaten to break the girls' bond, it only strengthens their commitment to the fantasy.

So far, so good. There is nothing stranger than the dream worlds concocted by adolescents in emotional turmoil, and director Jackson is more than happy to whip up the weirdness. Most of the girls' flights of fancy are communicated via scenes of the two of them running together, giggling as they strip to their underwear in the forest, or gleefully leaping through colorful, morphed-out hallucinations of The Fourth World, which come complete with fountains, castles and spooky clay men in gray latex suits. The camera swoops breathlessly, the music swells, and for brief moments you get a sense of how such impressionable souls could get so carried away.

And that's about all you get. The second half of Heavenly Creatures is a messy, overbearing and all-too-predictable escalation of events leading to a grim conclusion we already know in advance. The girls decide that Pauline's mother is to blame for their imminent separation, and irrationally decide that killing her will allow them to continue exploring The Fourth World together. This is a fascinating situation, but Jackson fails to supply a narrative angle to match; for all his directorial exuberance, he doesn't have a coherent point of view.

Stories similar to this one have worked because they aimed for a particular effect: River's Edge focused on the social decay surrounding a group of self-preserving kids who witnessed a murder and chose not to report it; Rope put us in the shoes of two men who killed out of academic whim, making us squirm as they slowly gave themselves away. With Heavenly Creatures, Jackson doesn't present his characters in any sympathetic or socially interested way--all he wants to do is marvel at their mental oddity, treating their slip into insanity less as a story than as an amusement-park ride.

Jackson's directing methods have served him well in less reality-based waters. His last picture, Dead Alive, is arguably the goriest, campiest, even sweetest zombie film ever created. That film (which, incidentally, also featured a character who does away with his mother) was so obviously silly that there was no need for Jackson to take any aspect of it seriously.

But with Heavenly Creatures, he's dealing with real people who brutally murdered a very caring, innocent mother. Jackson seems to know this, but he can't resist the temptation to camp up the proceedings with exaggerated, Monty Python-esque side characters; goofy one-liners (including the remark of a naive psychiatrist who assures the worried parents that the girls' love is just a phase, and that "medical science is progressing in leaps and bounds--there could be a breakthrough at any time!"); and even a nutty, nonsensical nightmare sequence in which the two girls are chased by a cackling Orson Welles. By the time of the murder, we aren't sure whether we're supposed to laugh, tremble, or shake our heads at the tragedy of it all.

Jackson's sensitive side doesn't always fail him, though, and he gets points for the repeated, psychologically disturbing image of the two girls resting opposite each other in a murky bathtub, with their heads poking out of each end like one big, self-absorbed organism.

Also good is the brief scene when Pauline's sister, observing Pauline and Juliet's fantasy-world chatter at the breakfast table, bitterly compares them to Laurel and Hardy. In one line, she shows more critical attitude toward Pauline and Juliet's shenanigans than Jackson has shown for the entire picture.

For all we know, Jackson is glad these two "heavenly creatures" forged a murderous liaison and gave him something weird to shoot. The film closes with a haunting, slow-motion scene of the two girls screaming as they're pulled apart for all time. If you listen carefully, you can almost hear Jackson screaming too.