It was the custom of the two main characters in Peter Jackson’s new film to refer to themselves in the third person as “heavenly creatures.” It’s probably fair to say, however, that the term wasn’t quite fitting.

Heavenly Creatures is based on the true story of two 15-year-old schoolgirls—Pauline Parker and Juliet Hulme—who planned and committed the brutal murder of Pauline’s mother in Christchurch, New Zealand, in 1954. The case generated sensational headlines, at least in part because it involved speculation that the girls were lesbians. The now-40-year-old crime acquired legendary status in New Zealand, where it’s also been subject to modern revisionism: Gay activists have cited it as an extreme example of what can result when parents attempt to discount or stifle their children’s homosexuality.

The film opens in 1952, when ungainly ninth-grader Pauline Parker (Melanie Lynskey) becomes aware of new classmate Juliet Hulme (Kate Winslet). Attractive, outspoken, and supremely self-confident, Juliet is everything that Pauline is not. When the two begin what at first seems an unlikely friendship, Pauline is worshipful of her new companion as only an insecure teen-ager can be. What the girls share, it turns out, is fertile imaginations, a propensity for escapism, and the capacity for obsessive behavior. The pair create their own imaginary kingdom, Borovnia, chronicling the activities of its royal family in meticulous detail. Naturally, the girls cast themselves as members of the dynasty, and they are soon corresponding in character, modeling likenesses of the royals in plasticine, and addressing each other by their “Borovnian” names. (The film touches upon without fully addressing the role of class difference in the girls’ friendship: To working-class Pauline, Juliet’s real life—she lives in a grand home and her parents are respected academics—seems as remote as Borovnia.)

Jackson’s background in campy science fiction and horror manifests itself as he depicts how these shared fantasies came to be more “real” to the girls than the world around them. The pair’s plasticine Borovnian figures grow to life-size, come alive, and whisk them into court festivities. The New Zealand hillside melts away, replaced by a land of unicorns and giant butterflies. Pauline and Juliet go to a movie, and its main character chases them home through the streets of Christchurch. The girls refer to their fantasy realm as “the Fourth World,” postulating that they are able to see it because “an extra part of our brain” allows them to. The pair’s capacity for make-believe quickly becomes sinister: Pauline, for example, loses her virginity while her consciousness is on hiatus in Borovnia.

In the film’s press kit, the director describes the saga as “a murder story with no villains,” suggesting that he intended Creatures as a sort of apologia for the girls. As such, it isn’t at all successful. Juliet and Pauline embody a host of typical teen-age traits: The girls are bored by their humdrum surroundings, captivated by film and music celebrities, impatient with their uptight parents, and insufferably smug (“How sad it is for other people that they cannot appreciate our genius,” writes Pauline). But the average obnoxious teen-ager is not a matricide. In their effort to establish their subjects’ commonality with other high-schoolers, Jackson and co-writer Frances Walsh neglect to adequately establish their differences. And it is the girls’ differences, of course, in which the audience is primarily interested. Though Jackson demonstrates the power of Pauline and Juliet’s fantasy world, he never effectively links that world to the evil that the girls eventually perpetrate. (After all, the Brontë sisters created an imaginary world, too—and well into adulthood—but rather than turning murderous they penned classics of world literature.)

Many of the girls’ actual comments—culled from psychiatric interviews, diary entries, and the like—are incorporated into Creatures‘ dialogue. These verbatim remarks—chilling in light of what occurred, yet also astonishingly immature—go a long way toward establishing that this is one story that didn’t need to be fictionalized to be made interesting. (Pauline’s diaries, filled with anticipatory references to “the day of the happy event,” got the girls arrested mere hours after the killing.) Like many films based on true stories, this one is far less interesting than its source material. Admittedly, though, there would have been less call for morphing and latex bodysuits were the film a documentary.

The tale’s most interesting sequel is one that Jackson did not include in the film’s epilogue. After serving her prison sentence, Juliet Hulme returned to England, where she resurfaced as “Anne Perry,” the author of a popular series of mystery novels set in Victorian London. The irony of it all? These workmanlike tomes—six of which were recently available at an area bookstore—belie the theory that “writing about what you know” is the key to compelling fiction. Jane Eyre they’re not.