Sophie Turner has joined the cast of the HBO Max series “The Staircase.”

Turner joins previously announced cast members Colin Firth, Toni Collette, Parker Posey, Juliette Binoche, and Rosemarie DeWitt.

The eight-episode series is based on the docuseries of the same name as well as various books and reports about the case of Michael Peterson (Firth), who was accused of murdering his wife, Kathleen (Collette), in 2001. He claimed she died after falling down the stairs at their home, but police suspected he bludgeoned her to death and staged the scene to look like an accident.

Turner will play Margaret Ratliff, one of Michael Peterson’s adopted daughters. Turner is best known for her role as Sansa Stark in the megahit HBO series “Game of Thrones.” Her time on the show earned her an Emmy nomination for best supporting actress in a drama. She is also know for playing Jean Grey in the latest entries in the “X-Men” film franchise, “X-Men: Apocalypse” and “X-Men: Dark Phoenix.” Most recently, Turner starred opposite Corey Hawkins in the Quibi series “Survive,” which debuted last year.

She is repped by CAA and Independent Talent Group.

“The Staircase” was picked up to series at HBO Max in March. It is written and executive produced by showrunners Antonio Campos and Maggie Cohn. Campos will also direct six of the eight episodes. The series is a co-production between HBO Max and Annapurna Television.

The docuseries was originally released in 2004, with creator Jean-Xavier de Lestrade updating with new information years later. Netflix released it as a 13-episode series in 2018. [Source]