The series focuses on the early and later life of Cassandra Austen (Keeley Hawes), and revolves around a literary mystery - Cassandra is notorious for burning the letters of her sister and close friend Jane Austen (Patsy Ferran). The story begins in 1830, many years after Jane Austen's death. Cassandra wants to help Isabella (Rose Leslie), the niece of her late fiancé, to save the house, but her real purpose is to find some of Jane's letters. She is worried that if these letters fall into the wrong hands, they will ruin Jane's reputation.