"What is the nature of history?" asks Irish writer Sebastian Barry. "Is it only memory in decent sentences, and if so how reliable is it?" His latest novel, "The Secret Scripture" (Viking, 300 pages, $25), suggests that most facts offered as historical truth are not only questionable but, he says, outright "treacherous."

It is 2006 and 100-year-old Roseanne McNulty has been confined to the Roscommon Regional Mental Hospital for most of her adult life. In her frosty, damp room she laboriously writes an account of her Sligo past, hiding the manuscript under the floorboards. The novel unfolds in alternating segments from her memoir and portions of a deposition recorded at the time of her commitment, which differs significantly from her account. That transcript is now in the hands of her psychiatrist, Dr. Grene.

Roseanne, for example, writes that her father was a cemetery caretaker and later Sligo's rat catcher, who hanged himself in a derelict cottage. Grene's information says that her father was a policeman with an "enormous capacity for alcohol" who was murdered by Irish Republican insurgents. The discrepancies loom large because Grene must decide whether she can return to society when the ancient hospital closes in a few months.

Barry writes with affection and sympathy for both characters. Grene marvels at Roseanne's endurance and suspects that she likes him just as much as he likes her. He is troubled that he finds himself so emotionally vulnerable around Roseanne, for reasons revealed later.

Clearly, emotion is at the core of Barry's splendid work, but to his credit the novel never becomes sentimental. His prose is impressively lyrical and evocative ("I sit here in my niche like a songless robin," says Roseanne, describing herself), but he also unflinchingly examines the serious mistakes -- some might say sins -- of the Catholic Church and the seemingly endless bloodshed and ruined lives from the Irish "troubles."

Perhaps most important, Barry conveys truths about human nature. As Roseanne writes, "The terror and hurt in my story happened because when I was young I thought others were the authors of my fortune or misfortune; I did not know that a person could hold up a wall made of imaginary bricks and mortar against the horrors and cruel dark tricks of time that assail us and be the author therefore of themselves."

Katherine Bailey also writes reviews for the Philadelphia Inquirer.