The story unfolds with a young woman named Emily Rose experiencing disturbing physical and spiritual phenomena that she believes are manifestations of demonic possession. After seeking medical help proves futile, Emily turns to her faith for answers. Desperate for relief, she agrees to undergo an exorcism conducted by Father Moore, a local priest who believes in the authenticity of her claims. The ritual, however, leads to tragic consequences, stirring a heated debate on the nature of faith, mental illness, and the law.

In the aftermath of the exorcism, Father Moore finds himself criminally charged with the negligent homicide of Emily. The case attracts the attention of Erin Bruner, a high-profile defense lawyer who takes on Moore's case in a bid to advance her career, despite her own agnostic views. As the courtroom proceedings unfold, the story delves into Emily's terrifying experiences through flashbacks and testimonies, challenging the skepticism of the legal system and the audience. The trial becomes not only a legal battle over the fate of Father Moore but also a platform for exploring the realms of science and religion, raising provocative questions about belief in the modern world.