"The Exorcism of Emily Rose," directed by Scott Derrickson from a script he wrote with Paul Harris Boardman, is a horror movie wrapped in a courtroom drama. A priest (Tom Wilkinson) is accused of negligent homicide because a young woman in his care has died after a failed exorcism. For the defense, we have Laura Linney, whose character, Erin Bruner, is an ambitious lawyer with somewhat better taste in liquor than in courtroom attire. For the prosecution, with gray at his temples and a neat little mustache riding his lip, there is Campbell Scott, whose character's steely patience eventually wears thin. "Your honor, I object," he exclaims, as every good courtroom-drama lawyer must. On what grounds? "Well, silliness, for one."

Sustained. But objecting to silliness in a horror movie is a bit unfair. The whole point of the genre - the fun as well as the terror - lies in the suspension of disbelief. "The Exorcism of Emily Rose," however, goes a bit further. Announcing from the start that it is "based on a true story" (words guaranteed to scare most movie critics), it tries to nudge its audience toward a real-world condition of belief in the supernatural doings it depicts.

Though Mr. Derrickson deploys the usual techniques of scary-movie making with a reasonable degree of competence, he does so for unusually high stakes. This is not meant to be just another spooky story, but rather a matter of (eternal) life and death, a religious argument decked out with dark and stormy nights, yowling cats and low-rent creep show effects.

The tale is fairly simple, and curiously lacking in suspense. We know from the start that Emily (Jennifer Carpenter), a devout 19-year-old who grew up in a rattling clapboard house in the middle of an empty field, is dead. The details of her last months are filled in by Father Moore (Mr. Wilkinson), who is either haunted by what he has seen or else suffering from chronic gas pain.

Mr. Wilkinson, usually a strong and subtle actor, here gives us no clue as to Father Moore's state of mind. Ms. Carpenter's Emily is a blank slate scribbled upon by diabolical forces. Though she flails and howls gamely, she is no Linda Blair. Her head does not spin, nor does she vomit green bile. Still, she does perform some extreme yoga poses, eats a handful of bugs and caterwauls in several languages, helpfully subtitled.

This leaves Ms. Linney to bear the burden of the drama, which she does with characteristic grace. Erin pronounces herself an agnostic, but stopped clocks and other ominous portents push her from skepticism toward acceptance of her client's view. Father Moore insists that Emily was in the grip of the Devil's minions, even as the prosecution presents an array of expert witnesses arguing that she suffered from a medical rather than a spiritual condition. Erin, in turn, unearths an anthropologist (Shohreh Aghdashloo) who studies demonic possession and is studiously noncommital as to whether it really exists.

The movie pretends to take the same tolerant, anything's-possible position. While not especially good - judged strictly on its cinematic merits, it ranges from O.K. to god-awful - it is still a fascinating cultural document in the age of intelligent design. Its point of view suggests an improbable alliance of postmodern relativism and absolute religious faith against the supposed tyranny of scientific empiricism, which is depicted as narrow and dogmatic.

The sincerity of a believer - Father Moore, in this case - is conflated with the plausibility of his beliefs. The doctors, meanwhile, seem so sure of themselves. But of course, the movie says, no one can ever be completely sure, and thus superstition becomes a matter of reasonable doubt. Meanwhile the clocks stop, the wind howls, and we are encouraged to believe - or at least not to disbelieve - our own eyes. Father Moore knows what he saw. So do I: propaganda disguised as entertainment.

"The Exorcism of Emily Rose" is rated PG-13 (Parents strongly cautioned). It has some harrowing scenes of demonic possession.

The Exorcism of Emily Rose

Opens today nationwide.

Directed by Scott Derrickson; written by Paul Harris Boardman and Mr. Derrickson; director of photography, Tom Stern; edited by Jeff Betancourt; music by Christopher Young; production designer, David Brisbin; produced by Tom Rosenberg, Gary Lucchesi, Mr. Boardman, Tripp Vinson and Beau Flynn; released by Screen Gems. Running time: 114 minutes. This film is rated PG-13.

WITH: Laura Linney (Erin Bruner), Tom Wilkinson (Father Richard Moore), Campbell Scott (Ethan Thomas), Colm Feore (Karl Gunderson), Jennifer Carpenter (Emily Rose), Mary Beth Hurt (Judge Brewster), Shohreh Aghdashloo (Dr. Adani), Joshua Close (Jason), Kenneth Welsh (Dr. Mueller), Duncan Fraser (Dr. Cartwright), JR Bourne (Ray) and Henry Czerny (Dr. Briggs).