"Ravenous" is a dark comedy thriller about cannibalism at an army post in the pre-Gold Rush Sierra Nevada. It's one of those high-concept movies that is easy to pitch to a studio head in 25 words or less by combining two ideas into a sentence, in this case, "'Dances With Wolves' meets the Donner party."

Originally envisioned as more horror than parody, 20th Century Fox changed directors early on because they wanted to emphasize the humor angle, as the script was already rich with subtle irony -- it uses cannibalism as a metaphor for Manifest Destiny and drug addiction.

As a result of the change, the movie is often uncertain which way it wants to go, but once it finds its footing, the comedy elements mix successfully into what is essentially a abstruse thriller.

"Ravenous" stars Guy Pearce ("L.A. Confidential") as Captain Boyd, a cowardly army captain and accidental Mexican-American war hero, who is assigned to a California mountain fort full of oddball enlistees during the winter of 1847. There he helps rescue a pioneer named Colqhoun (Robert Carlyle, "The Full Monty"), who tells a harrowing tale of settlers trapped by a snowstorm who turned to cannibalism to stay alive, then developed an insatiable appetite for human flesh.

This campfire tale scene sets the mood for the film, Carlyle gripping both his on-screen and off-screen audiences with all-too-vivid storytelling in the dungeon-like setting of the cold and dreary fort. "Things got out of hand," he whispers. "I ate sparingly. Others did not."

The fort brigade, lead by commanding officer Hart (Jeffrey Jones), sets off to find the cave where the settlers put in and hopefully rescue whatever is left of them, but Colqhoun isn't quite what he seems and the rescue becomes something of a massacre, leaving Boyd having to find his way back to the fort alone and with a badly broken leg.

"Ravenous" has several delicious (pardon the pun) twists, and I don't want to give too much away, but suffice to say Boyd starts to feel the overwhelming urge to partake in ritualistic cannibalism after making a survival decision in the wake of the cave carnage. Then, when he makes it back to the fort he finds his new commanding officer is no stranger to this same hunger.

The second half of the film is a matter of Boyd's strength to resist this compulsion, and Pearce is brilliantly uncertain in his conviction.

(Spoiler warning!)

Carlyle also give a calculating, evasive performance as the frightened settler who turns out to be a startling kind of monster. There's an "Interview with the Vampire" element to the relationship between these two men, Carlyle being something of a Lestat to Pearce's Louis.

After a bit of comedic unease in the early going, director Antonia Bird, who worked with Carlyle on "Priest," successfully balances the film with ironic humor while maintaining a frightful facade that likens itself to another movie about a mad cannibal -- "Silence of the Lambs."

Aided by a oddly playful yet creepy accordion-and-banjo score by Michael Nyman and Damon Albarn, "Ravenous" is a little impudent in what it finds funny, but eventually settles into a facetious, Coen Brothers-style sense of humor.

Meanwhile, the darker elements of the movie make sport of the fear the film has been building in the audience, taking cues from horror movies for the last act showdown between reluctant hero Boyd and not only his cannibalistic nemesis, but his own growing appetite for flesh.

Director Bird makes good use of the winter setting, bringing forward the harshness of the elements and giving every scene a cold, uncomfortable air that helps keep the audience edgy. And while the comedy seems questionable at first, she manages to bring it nicely into balance with the psychological terror at the center of the story.

"Ravenous" is definitely not a movie for those who don't consider themselves blessed with a sick sense of humor, but if you think you can stomach the topic of cannibalism with all it's visual accouterments, it is an appetizing thriller.