Edinburgh, 1810. Teachers Jane Pirie and Marianne Woods embark on their dream of an independent life together and open a boarding school. Their lives are changed forever when a wealthy aristocrat enrols her 'illegitimate' 15-year-old grandchild from India. The teachers struggle to integrate the girl who remains an outsider among her classmates.

Miss Pirie and Miss Woods are brought closer to Jane Cumming when her grandmother insists they look after her over the summer. Private and professional lines blur, affection between them grows and they start to form an unlikely family. Tensions rise as the new term begins. The teachers are overwhelmed with the girl's increasing desire for closeness and their own changing relationship. As Jane Cumming begins to feel excluded from her new family, she demands to be taken home to her grandmother. An accusation follows which leaves the teacher's fighting for their lives, resulting in a legal battle that would last a decade and scandalize the Scottish establishment. Based on true events.