Secret for a Nightingale by Victoria Holt

Secret for a Nightingale - Susanna Pleydell began her life in India where she 1st learned of her ability to aid the ill. However, she meets Aubrey St. Clare and is swept off her feet. But Aubrey has an obsession that she cannot participate in. Susanna leaves her husband, changes her name and begins her life as a nurse which brings her into direct contact with the man she blames for getting Aubrey into drugs and ruining his life and as well as hers. During the Crimean War she comes face to face with her declared enemy.