 The nineteen years old Catholic college girl Emily Rose (Jennifer Carpenter) dies a couple of days after being submitted to an exorcism carried out by her parish priest, Father Moore (Tom Wilkinson). Emily believed she was possessed by six demons, and although authorized by Emily and he parents, Father Moore is accused of negligent homicide, since he had suggested Emily to interrupt the use of medications for epilepsy. In order to avoid a scandal, the Archdiocese hires the successful, ambitious and agnostic lawyer Erin Bruner (Laura Linney), and the prosecution assigns the religious prosecutor Ethan Thomas (Campbell Scott). Along the days, there is a battle between science and religion in the court.