Once There Was A Nun: Mary McCarran's Years As Sister Mary Mercy is a biographical book written by Ruth Shick Montgomery. The book tells the story of Mary McCarran, who became a nun in the early 1900s and spent over 30 years in service to the Catholic Church. The author uses McCarran's own words and experiences to paint a vivid picture of her life as a nun, including her early years in the convent, her work as a nurse, and her eventual departure from...