In a spur-of-the-moment decision made in the chaos of a crowded Edinburgh railway station at the start of World War II, two young evacuees trade places, names and lives. Shy, wealthy Marjorie Malcolm Scott, on her way to stay with relatives in Canada, becomes Shona McInnes, an adventurous orphan bound for a small town in the south of Scotland. Neither girl foresees that the war will last for six years.
In taking Shona's name, Marjorie inherits a battered suitcase containing Shona's only possessions—a few shabby clothes and an oil painting of a large Victorian house, Shona's only clue to her past. Marjorie also has charge of Anna, a backward child from the orphanage who was assigned to Shona's care.
Marjorie and Anna are billeted with two kindly, but eccentric, middle-aged sisters. Despite the hardship of war, Marjorie's life as Shona is happy in ways it never was before. But as she makes plans for the future, the question of who she really is haunts her, and at the war's end she knows she must search for the real Shona and settle the question of her identity.