In an extremely rare decision, the Catholic Church officially recognized the demonic possession of the 19 year-old college freshman. Told in flashbacks, The Exorcism of Emily Rose chronicles the haunting trial of the priest accused of negligence resulting in the death of the young girl who is believed to be possessed and the lawyer who takes on the task of defending him.
Lawyer Erin Bruner (Laura Linney) takes on the church and the state when she fights in defense of a priest, Father Richard Moore (Tom Wilkinson) who performed an exorcism on a young woman, Emily Rose (Jennifer Carpenter). Bruner must battle the state lawyer as well as her own loneliness, as she realizes that her career so far has not fulfilled her. She takes the case, albeit reluctantly, because she believes it will elevate her to senior partner at her law firm. The priest agrees to let her defend him only if he is allowed to tell Emily's story.
The trial begins with the calling of several medical experts by the prosecutor, Ethan Thomas (Campbell Scott). One expert testifies that Emily was suffering from both epilepsy and psychosis. The defense contests that she may have actually been possessed, though Bruner is careful never to say that in so many words intially. Indeed Bruner explains that Emily was suffering from something that neither medicine nor psychology could explain, and that Father Moore as well as her family realized this and tried to help in another way. Several flashbacks show how this began. Alone in her dorm room one night, at 3:00 AM, she smells a strange burning smell from the hallway. When she checks on it, she sees the door open and shut by itself several times. When she goes back to her room, she sees a jar of pencils and pens move by itself. Additionally, her covers roll themselves down, and a great weight seems to press down on her, a force which also proceeds to choke her and seemingly to possess her momentarily. Through these episodes she wonders if they are really happening or if it is just a hallucination she is experiencing. She suffers more "visions", is hospitalized, and diagnosed with epilepsy. She is given anti-seizure medications which she claims do not work. Her visions continue, as do her severe bodily contortions.
She leaves school and returns to live with her parents. She and her parents become convinced she is not epileptic or mentally ill but is possessed by demons. They ask for their local parish priest to be called in to perform an exorcism, and the Church agrees. The prosecution counters that all this could be explained by a combination of epilepsy (the contortions) and psychosis (the visions).
Meanwhile, Bruner begins to experience strange occurrences in her apartment at 3:00 AM, including strange smells and sounds. Father Moore warns her that she may be targeted by demons for possibly exposing them. Later in the film Father Moore explains that 3:00 AM is the "witching hour" which evil spirits use to mock the Holy Trinity. Significantly, it is the opposite of 3:00 PM, traditionally taken to be the hour at which Jesus died.
Seeing that the prosecution is putting up a seemingly solid medical case, Bruner decides to try to show that Emily may have actually been possessed. She calls in an anthropologist, Dr. Sadira Adani, to testify about various cultures' beliefs about spiritual possession.
A medical doctor present during the exorcism comes forward to reveal an audio tape made during the rite. The priest is then called to the stand to testify. The tape is played and the movie then flashes back to the exorcism. It is performed on Halloween night because Father Moore believes it might be easier to draw out the demons on that night. The priest, Emily's boyfriend, and her father are in the room. Emily is tied to the bed. The priest uses holy water and various words from the Rituale Romanum. She speaks in tongues, including Latin, German, Ancient Greek, Hebrew, and Aramaic. Several cats run into the room, jumping on the priest and knocking him down. Emily breaks her ties and jumps out the window, running into the barn. They follow her. Inside the barn, they are subjected to more supernatural phenomena such as unnatural gusts of wind and demonic screams and voices. The demon inside Emily refuses to name itself after repeated demands from the presiding Father but finally reveals contemptuously that there are not one but six demons. They go on to identify themselves in dramatic fashion, naming themselves one after another in dual voices from Emily. They identify themselves as the demons that possessed Cain, Nero, and Judas Iscariot and one of the Legion. Beyond that two demons name themselves directly as Belial, and "Lucifer, the devil in the flesh."
The film returns to the court room. The priest says that after this, Emily refused another exorcism but also refused to take her anti-psychotic medication, having accepted her fate. She died a few weeks later. The prosecutor contends that her speaking in tongues can be explained by her having gone through Catholic Catechism, in which she could have learned the ancient languages, and that she had studied German in high school. The priest admits that it might be possible that she could have learned these languages in school.
Bruner then wants to call the doctor as a witness, but he does not show. She walks outside and sees him on the street. He says he can no longer testify, but he does believe in demons. Before he can explain he is hit by a car and killed. Later that night Bruner's boss tells her she has ruined the whole trial and that if she recalls the priest to the stand she will be fired.
Nevertheless, Bruner calls the priest back to the stand the next day. He reads a letter that Emily wrote him before she died. In the letter Emily describes another vision she had, the morning after the exorcism. She walks out of the house and sees the Virgin Mary, who tells her that although the demons will not leave her, she can leave her body and end her suffering. However, the apparition goes on to say, if she returns to her body she will help to prove to the world that God and the Devil are real. She chooses to return. She concludes the letter by saying "People say that God is dead, but how can they think that if I show them the Devil?" She then receives stigmata, which the priest believes is a sign of God's love for her, but the prosecution counters that she could have received the stigmata wounds from a barbed wire fence on her property.
Father Moore is ultimately found guilty; however, on a recommendation from the jury, the judge agrees to a sentence of time served. In modern American legal practice, juries are only allowed to answer questions specifically directed to them, though sometimes they are asked separately to sentence defendants. The jury's recommendation in this fictional case does not follow American practice.
Bruner is offered a partnership at her firm for saving Father Moore from extended jail time, but she refuses and in fact quits. She goes with Father Moore to Emily's grave, where he has put a quote (which she recited to him the day before she died) from the second chapter twelfth verse of Philippians on her grave: "work out your own salvation with fear and trembling".