The best thing about The Mist is the miasmatic fog itself, an oily grey soup of propylene glycol that roils across the film’s sets like hell broth spilled from a witch’s cauldron. Unfortunately, Frank Darabont’s adaptation of Stephen King’s 1980 novella is just as thick and smarmy. This scary story about a small town smothered by a bilious brume metamorphoses into an earnest morality tale; the film promises gnarly B-movie goosebumps but delivers an unctuous salve on noisome human nature.

Darabont is celebrated for two earlier adaptations of King, The Shawshank Redemption and The Green Mile, metaphysical prison dramas, and The Mist might be described as metaphysical horror. True to the genre, the director delivers a mélange of creepy crawlies that sting, gnaw and zap their way through a reel of stock shock scenes. Darabont, however, is searching for the philosophical lining in this pestilential cloud. When panicked villagers inevitably split into warring factions, courage and reason must struggle against fear and prejudice as well as the entomological vapor.

After a fierce storm cuts power to a rural stretch of Maine, commercial illustrator David Drayton (Thomas Jane) and his boy, Billy (Nathan Gamble), head to the supermarket to stock up on supplies. Most of their neighbors, a mixture of yokels and yuppies, have the same idea. Everyone is full of good will and best intentions until Dan Miller (Jeffrey DeMunn) comes charging across the parking lot with blood streaming from his nose, shouting incoherently about the mist drifting inland from the lake…terrible things in the mist.

It takes a scream from the gloom for these stoic Mainers to heed Dan’s warnings, but they pile into the store and lock the doors against the mysterious fog. But the mist, and the creatures it shrouds, isn’t so easily deterred. Mucilaginous tentacles find their way under the loading dock doors, lassoing a hapless stock boy and dragging him off to another dimension. By nightfall, hybrid arthropods—half locust, half scorpions—are banging their carapaces against the market’s plate-glass windows, closely followed by bat-like pterodactyls and crustaceous spiders spewing radioactive gossamer.

David, a freelancer accustomed to onerous work conditions, attempts to organize the survivors against the siege, supported by feisty store manager Ollie (Toby Jones) and compassionate schoolteacher Amanda (Laurie Holden). Predictably, the terrified townies instead turn to Mrs. Carmody (Marcia Gay Harden), an uptight, Bible-quoting hypocrite—we know she’s evil because she’s the only character addressed with an honorific. Mrs. Carmody rapidly evolves from nuisance to doomsday prophet demanding sacrifice. (She’s an Old Testament kinda gal.) Naturally, her hysteria sparks a lively discussion about human nature and such:

“People are basically good,” argues Amanda, unwilling to believe Mrs. Carmody means bad.

“Sure, as long as the machines are working and you can dial 911,” counters David. “No more rules, you’ll see how primitive they get.”

Scintillating as this exchange is, The Mist must move on, since Darabont has to sort out the military machinations behind the whole business (still another secret experiment gone awry) and get his characters to safety. But don’t expect happily ever after…this movie has the most downbeat ending since James Brown gave up the groove.

The Mist has all the ingredients for a fun, if derivative, monster movie, but it makes the fatal mistake of taking itself seriously. Have bedrock Americans gotten paranoid in the fog of the war on terror? Will people lose their sense of proportion if you scare them badly enough? Like the bugs that continue to grow in size as the film progresses, The Mist inflates its response to honest but simple questions.