In 1856, fresh from life with nuns in an orphanage school, Alexina Barbin comes to a coastal village in La Rochelle to teach the village girls. She is deeply religious. She shares the classroom and a bedroom with the young and vivacious Sara, with whom she falls in love. Alexina has another secret: her gender is mysterious. She and Sara begin a scandalous love affair, but Alexina seeks marriage and social acceptance. She discloses her secrets to the village priest, to her mother, to the bishop, and to the bishop's physician. After the church and court rule on her petition, marriage to Sara becomes Alexina's sole purpose and hope.