The Rev. Moore (Tom Wilkinson) is prosecuted for the wrongful death of a girl thought to be demonically possessed, because he administered the church-sanctioned exorcism that ultimately killed her. Prosecuting attorney Ethan Thomas (Campbell Scott) contends that the young woman, Emily (Jennifer Carpenter), suffered from schizophrenia and should have been medically diagnosed. Meanwhile, defense lawyer Erin Bruner (Laura Linney) argues that Emily's condition cannot be explained by science alone.