Aside from a “based on a true story” claim, The Exorcism of Emily Rose dares us to disbelieve by listing doctors as consultants to the story.

Too bad this slogging, slow two-hour movie unfolds like a visual version of a dry doctoral thesis in paranormal studies. It wants to be sterner and more serious than the average horror movie, but gets fatally lost in its own babble.

By examining a failed exorcism’s aftermath in a courtroom setting, Emily Rose would like to combine John Grisham’s convoluted legalese with Dean R. Koontz’s faith-oriented spooks. Too bad both authors’ pulpy jolts have been expelled from the body of this retro-horror wannabe.

The best to be said of the usually excellent Laura Linney is that she boasts her best onscreen tan since Congo. She stars as Erin Bruner, a junior-partner lawyer who “wants her name on the door” in exchange for defending the touchy, tricky case of fallen priest Father Moore (Tom Wilkinson).

He’s on trial for negligent homicide in the death of Emily Rose (Jennifer Carpenter), a college student allegedly possessed by the devil who died after Moore’s arduous, unsuccessful exorcism. Naturally, as Moore tells Erin, “evil forces surround this trial,” as does mow-’em-down prosecutor Evan Thomas (Campbell Scott, who barely bothers to twirl his Charlie Chaplin-style mustache).

The problem with director Scott Derrickson’s interminable courtroom scenes is that he intends for them to be taken seriously when they are, in fact, caricatures. That would be fine if any of the actors appeared genuinely in creating cornball fireworks. There are brief objections and conferences at the bench, but there is plenty of bloated banality in all of the witness questioning.

Nearly all of Emily Rose feels like good actors getting together on a lark for a fat paycheck. The Exorcist boasted fine actors, too, but it was in-your-face provocative where Emily Rose is bumbling and pedestrian.

All these actors had to do was recite courtroom dialogue and occasionally rise from sleep to experience some spookiness at 3 a.m., this horror movie’s appointed Time At Which Spooky Things Happen. (Father Moore even sucks the fun out of that with his overly mannered explanation.)

Whenever the movie attempts to wrack the nerves, it recycles The Exorcist’s beats — the devil’s image in the windowpane, freaky bone cracking and body bending, girlish waifs speaking with old man’s voices. About all Emily does differently from Regan is not suggesting what Father Moore’s mother might do in hell. This is, after all, a PG-13 movie.

Like other mostly bad PG-13 horror movies, Derrickson tries to attach scary atmosphere to everyday objects, such as turkey, pie and pigeons. Later, Emily becomes able to command cats to do her bidding and instigates a horse stampede for no other reason than that the film needs action.

Derrickson also cuts to a silly flashback during the movie’s most interesting moment and rips off one camera trick from Requiem for a Dream. Maybe it’s to be expected from the co-writer of Urban Legend: Final Cut. His and Paul Harris Boardman’s script has delectably dumb lines like “I never knew how dead I was until I met her” and “The forces inside her. Y’know, the demons.”

The movie’s attempt to have a fuzzy Christian feel at the end rings false as well. It’s hard to feel Emily’s spiritual struggle when we see her as a normal girl for all of 30 seconds before she becomes a vehicle for gory makeup and visual effects. Unquestionably, this is one of the year’s worst movies.