Half-sisters Elizabeth, Anne and Janie Temple have been left orphaned and poor by the death of their father, a Naval Captain, five weeks before the story opens. Elizabeth and Anne are the daughters of Captain Temple's first wife, Giovanna, and Janie is the child of his second marriage.
Following the death of Janie's mother, the three girls go to school together until Elizabeth is eighteen, Anne fourteen, and Janie nine; then when the school closes, as Captain Temple is away at sea (towards the end of 1918), they find a home in France with Madame Ozanne, the mother of his first officer. They remain there for five years, during which time their various talents are carefully nurtured, until they return to England to live with their father, who has now retired from the Navy.
When Captain Temple dies, Elizabeth decides that the three of them should move to Guernsey, where Madame Ozanne's old nurse, Javotte, has a small cottage which they can rent. Their scanty income will go further in Guernsey than in London, and between them they can teach Janie, since school fees are beyond their means. Accordingly, Elizabeth goes over to make the arrangements, and a little later her sisters set out to join her. They take up residence at La Rochelle, Javotte's cottage, and begin getting to know their neighbours.
Elizabeth meets a little girl, Pauline Ozanne, whose brother Paul lives in St. Peter Port. Later, Pauline and Janie do lessons together. They also become acquainted with Doctor Chester, who comes to see their neighbours, the De Garis family. Janie has an encounter with La Sorcière Blanche, a local wise woman. In the summer, they all make friends with the numerous members of the Atherton family who are staying nearby for the holidays.
Despite the melancholy beginning and some hair-raising events, the story ends happily for all three sisters, and features or mentions many characters who appear in the Chalet School stories.