Roseanne McNulty, once one of the most beautiful and beguiling girls in County Sligo, Ireland, is now an elderly patient at a mental hospital. As her hundredth year draws near, she decides to record the events of her life but hides the manuscript.

Meanwhile, the hospital is preparing to close and is evaluating which patients can return to society. Dr. Grene, Roseanne's caretaker, takes a special interest in her case. In his research, he discovers a document written by a local priest that tells a very different story of Roseanne's life than what she recalls. As doctor and patient attempt to understand each other, they begin to uncover long-buried secrets about themselves.

Set against an Ireland besieged by conflict, The Secret Scripture is an epic story of love, betrayal, and unavoidable tragedy.