Orphaned as a young child, Emma Booth was raised by her grandparents in a Lancashire village. Following her grandfather's sudden death, Emma assumes she is now without family, until she finds a letter written in 1940 from a woman to her widowed father. The letter reveals that before his death at Dunkirk, her father had fathered another child, and that Emma has a half-sister, Betty Booth . Determined to find Betty, Emma is drawn away from the countryside to the austere city life of post-war Liverpool. But building a relationship with Betty isn't easy, and Emma has to overcome dogged obstruction from Betty's aunt, Elsie, to be a part of her sister's life. Despite the challenges, the sisters discover common ground and get along well, until a secret threatens to disrupt their newfound relationship and life together