The movie was filmed in British Columbia, Canada and takes place in America in what looks to be the early oughts. The real story took place in Germany in the 1970's. About the only thing that stays the same is that the young woman being exorcised ended up dead. Her real name wasn't Emily Rose. The priest conducting the exorcism was tried for negligent homicide, so that's sort of right. Why not go with a complete fiction? Because 'Based on a true story' is part of the selling point for a movie like this.
So a devout young woman from a rural area goes to a big city college and gets possessed by a Devil. Or maybe The Devil. No, maybe it's six devils piled into her like she's a clown car. And they're all really important devils, name-checking their importance. Or maybe they're lying. Mean old medical science decides Emily Rose is epileptic, prescribes drugs.
Oh ho, we're told by an anthropologist called in for the homicide trial, those epilepsy drugs made Emily Rose MORE SUSCEPTIBLE to demonic possession! Because God didn't account for the invention of pharmaceuticals or something. Also, the expert witness anthropologist quotes Carlos Castenada on the stand. I kid you not. She also appears to be Hindu. Theologically speaking, I have no idea what that means.
Laura Linney plays the agnostic defence attorney who learns to believe in something after being stalked by a demonic presence throughout the trial because Dark Forces want a certain trial outcome! The demons like to wake people up at 3 a.m., I'd assume because they're doing a riff on The Amityville Horror. The devil, or a devil, occasionally shows up as a silhouette of what appears to be Emperor Palpatine.
One thing that gets me with works like this is that they make no sense from the standpoint of the very religion they purport to champion. Father Moore (a beleaguered Tom Wilkinson, earning that paycheck) theorizes that God wants him to stand trial so that people will hear Emily Rose's story and thus find proof of God. But proof negates faith. If God had ever wanted proof to be a component of Christianity, then He's been going about it the wrong way for more than 2000 years. This is an advertisement for Roman Catholicism from people who don't seem to have the faintest idea what Roman Catholicism stands for.
Anyway, the movie makes it clear that there's a possession going on, and that Emily Rose died not as a result of the exorcism but as a result of the demons getting stuck inside her because of her anti-epileptic medication. And it's all true, even though it isn't. How many people die in exorcisms every year? What a self-righteous, morally reprehensible turd of a movie. Everyone involved should be ashamed. Not recommended.