Miss Austen comes to a close in a two-part finale airing back-to-back this Sunday, May 18, on PBS. The Masterpiece adaptation of the novel of the same name tells the story of what led Cassandra Austen to burn the letters of her sister, beloved author Jane Austen — an act that has left Cassy often painted as a villain in history books. But the true “soulmate” relationship between these two sisters, as star Keeley Hawes describes it to TV Insider, is at the root of everything in this tale, and Hawes says the central conflict of the show’s present-day timeline is going to reach a surprisingly “gentle” conclusion.

Set many years after the death of Jane, Miss Austen shows Hawes as Cassandra, a woman who never married out of a commitment to her fiancé who tragically died before they could wed and to her sister, the closest relationship of her life. The flashbacks show how close Jane (Patsy Ferran) and Cassy (Synnove Karlsen) were and the reasons why Cassy felt she had to stay single in order to take care of her family. Neither she nor Jane ever married; they lived their days together, and Cassandra could never bring herself to leave her sister behind no matter how profound a love came knocking.

The most pressing conflict in the present-day timeline is between adult Cassy (who’s been aged down by decades for the purposes of this story — in reality, Cassandra was in her 70s when she burned the letters) and her acidic sister-in-law, Mary Austen (Jessica Hynes). Mary was married to Jane and Cassy’s brother, who was also an author. And she wants history books to remember James Austen as the better writer of the family. Cassy fears what Mary would do with Jane’s letters to their late friend Eliza, mother to Rose Leslie‘s Isabella, who, like Jane and Cassy did in their youth, is unmarried and facing housing and financial insecurity following the death of her father at the beginning of the series.

Cassy found Jane and Eliza’s letters and discovered that young Mary (Liv Hill) lied to their entire social circle about how Cassy reacted to the death of her fiancé. The delayed discovery of this betrayal broke Cassy’s heart and worsened the lack of trust that already existed between these two women. Mary, therefore, can’t be trusted with the contents of Jane’s letters.

Cassy and Mary have been squabbling throughout all of Miss Austen‘s two previous episodes. In the final two episodes on May 18, Hawes says that their rivalry “comes to a head in a very satisfying and quite a gentle way, rather than an explosive way, I would say. We shot our final scene together, and it was really hard to hold it together, and the reason being that they kind of go their separate ways ultimately.”

Hawes implies that forgiveness comes because these women don’t know if this meeting will be their last.

“Their parting happens, and Cassandra has to go back to her life, and they all have to go back to their lives and they say goodbye. But being women of that age where people didn’t live for a terribly long time either, when Cassandra is saying goodbye to Mary Austin, they don’t know when they’re going to see each other again, if ever. And that brings it into sharp focus that they do care about each other. They really do care about each other, and they have this history together, and along with that is all of its loves and losses and life and bereavements and all the other things that happen in the space of a lifetime. But it was really, really difficult to see. It was one of the trickiest scenes to say goodbye to Mary Austen.”

“I was sort of slightly in bits, had to reign myself in a bit,” Hawes explains of the difficulty of the scene. She says that it was difficult to stifle Cassy’s emotional responses in this scene, a necessity for the character. Her natural inclination is to fully lean into the emotion of the moment, but the social norms of this time period — and the essence of her character in general — required more holding back. Seeing Mary show signs of deep feeling but having to swallow them as well also informed the heightened emotional experience of this scene.

“It’s very moving, the idea of [saying goodbye to someone for the last time],” Hawes says. “And also someone who is afraid to — well, isn’t good at showing their emotions like Mary. To feel that [emotion], that they’re feeling it very deeply, but are unable to show it, it’s actually much worse.”

These women are the only sisters each of them has left, which is a tragic irony for both of them. But some sisterly affection could be the exact kind of healing both of them need.

Miss Austen, Two-Part Series Finale, Sunday, May 18, 9/8c, PBS