Roseanne Clear McNulty, a patient at Roscommon Regional Medical Hospital. Dr. William Grene has been her psychiatrist for 24 years. Roseanne is nearly 100 years old but doesn't know her true age. She was first a patient in Sligo Mental Hospital, nicknamed Leitrim Hotel because of its large population of Sligo citizens. Roseanne's in-laws, the McNultys, who were employees at the hospital, worked with Father Aloysius Mary Gaunt, a stern local priest, to have her committed there. While growing up, Roseanne was close to her father, Joe Clear, a Presbyterian who worked as a superintendent at a Catholic cemetery in Sligo. Joe Clear entertained Roseanne with stories, many of them about his years in the British Merchant Marine.

While Roseanne writes her personal history, or "testimony," Dr. Grene writes his observations of her in his commonplace book. The narrative shifts between these two characters, whose seemingly disparate lives converge as the novel progresses. Dr. Grene is eager to question Roseanne to learn more about her, but he doesn't want to offend her because of his fondness for her. John Kane, the custodian at the asylum, also looks after Roseanne.

In her youth, Roseanne travelled along with her father, Joe, when he served as superintendent at Sligo's Catholic cemetery. Father Gaunt later fired him from the job for helping the anti-treaty rebel, John Lavelle, bury his murdered brother, Willie Lavelle. Father Gaunt gives Joe Clear a job as a rat-catcher instead. One day, while working at an orphanage, a paraffin-soaked rat escaped from Joe's grip before he could throw it into a bonfire with the other rodents. The rat later caused a fire which burned down the orphanage. Meanwhile, Roseanne's mother, Cissy Clear, descended further into madness and, in Roseanne's memory, her father hung himself. Dr. Grene, however, one day reads Father Gaunt's deposition, which claims that the Irish Republican Army (IRA) murdered Joe, in revenge for his previous activities with the Royal Irish Constabulary (RIC).

Later, Father Gaunt visited Roseanne to convince her to convert to Catholicism and to marry the much older Joe Brady. She refused, and Father Gaunt resented her for her perceived stubbornness. While learning these aspects of Roseanne's story, Dr. Grene thinks about his estrangement from his own wife, Bet, because of his affair with a colleague. Bet died as a result of her poor health. After telling Roseanne the news, she comforted him, which surprised Dr. Grene.