With no money of her own and little hope of selling any of her unfinished manuscripts, Jane Austen accepts a marriage proposal from the heir to an estate in her beloved Hampshire, only to break her engagement the following day because she does not love him. She chooses to devote herself to writing fiction, even though she may always have to depend on her parents or brothers for money. When Fanny Palmer falls in love with Jane's brother Charles Austen, a handsome captain in the Royal Navy, she sees herself as the heroine of a romantic story and chooses to accept his proposal of marriage even though he has very little money. She shares her husband's desire for children and his confidence that he will soon increase his income by capturing naval prize ships, and she insists on travelling with him when the squadron sails to Nova Scotia, instead of staying at home in Bermuda.

Exchanging letters across the Atlantic during the tumultuous years of the Napoleonic Wars, Jane and Fanny become close friends. They share in each other's sorrows as Jane struggles to publish her novels and Fanny confronts her fears about pregnancy, childbirth and the dangers Charles faces at sea. But the friendship begins to fracture after Charles brings his family to England, as Jane and Fanny discover disagreements over issues they haven't talked about in their letters, including how best to care for children. When Jane starts to find success as a writer, Fanny admires her novels about romance and courtship, yet her anger at her sister-in-law's refusal to write about the challenges of marriage and motherhood and the risks of childbirth threatens their friendship.

Like Maggie O'Farrell's Hamnet and Colm Tóibín's The Master, The Austens explores tensions and rivalries between a great writer and the people closest to them.