Certain very good actors have an excellent eye for trash. Laura Linney might have 20/20 vision, based on her parts in ''Congo," ''The Mothman Prophecies," and, most outrageously, ''The Life of David Gale," in which she played a homely yet extreme political activist. The fun of these movies is that Linney often seems too refined for such greasy junk, but there she is anyway, hamming it down as it were.
Linney is more or less the star of ''The Exorcism of Emily Rose," a perfectly sorry excuse for a horror film that casts her as Erin Bruner, an uptight, top-flight lawyer who's defending a priest (Tom Wilkinson) accused of killing a young woman (Jennifer Carpenter) in a bid to rid her of unholiness.
Most of the movie is set in a courtroom, so Linney has very little to do with the tasteless flashbacks to Emily's affliction. But the movie is a tale of double possession. Erin is crazed about her career. Yes, this is one of those movies about a woman whose only ambition is making partner. She goes to bed alone, in a sterile home, has no friends, and eats, sleeps, and breathes her case, which plays like an extra devilish episode of ''Law & Order."
The archdiocese specifically requested Erin to defend Wilkinson's Father Moore. She recently got an accused murderer acquitted, and her star is on the rise. But the Catholics don't know -- she's agnostic. In a sense, this is ideal for her line of defense: I can't prove Emily was possessed, but, hey, I can't prove she wasn't.
Of course the movie, which claims to be based on a true story, seems to believe she was. We see poor Emily, a recent college freshman from a rural town, pinned back in her bed, an invisible force atop her body, strangling her. She flips out in class, much the way the teen paranoids did in those ''Nightmare on Elm Street" films, and runs across campus shrieking in the rain in a nightgown. She sees ghoulish faces on her classmates, and hears heavy breathing. She eats bugs, speaks in tongues, and contorts her body into a satanic yoga pose best described as downward demon. Look for the Emily Rose training regimen at your local Healthworks.
The district attorney -- a starchy Campbell Scott, in what appears to be a stunt mustache -- claims Emily was suffering from a psychotic bout with epilepsy. She died of malnutrition and nasty physical trauma, he says. As a rebuttal, Erin later calls to the stand an expert in the ''science of possession" who is played by the regal Oscar nominee Shohreh Aghdashloo. The actress answers a few questions and then is free to cash her check.
Scott Derrickson directed and, with Paul Harris Boardman, wrote ''The Exorcism of Emily Rose." He and Boardman also wrote the cheeky 2000 sequel to the teen slasher flick ''Urban Legends." The horror impulse that grips the filmmaking -- full moons, ''gotcha" editing, pigeons that act like bats, things going bump in the night -- is mostly just cheap tricks.
''There are dark forces surrounding this trial," Father Moore tells Erin. ''Demons exist whether you believe in them or not." But the movie never makes good on his promise.
The material cries out for the craftsmanship of ''The Exorcist," which this movie is desperate to evoke. Linney has never looked foxier, and she uses good diction and her Ivy League carriage as weapons against some of the more laughable scenes. (See her face after a car hits her star witness!)
The preposterousness of the trial, which is never lost on Scott's lawyer, has its pleasures, too. At one point, Scott objects to a line of questioning. ''On what grounds?" asks the judge. ''Silliness."
Wesley Morris can be reached at email@example.com.