The Staircase” series at HBO Max has cast Odessa YoungVariety has learned.

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

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.

Young will play Martha Ratliff, one of Michael Peterson’s adopted daughters. Her role in the series reunites her with Firth, with whom she stars in the upcoming feature “Mothering Sunday,” based on the Graham Swift novel of the same name from director Eva Husson and writer Alice Birch. The film will debut at the Cannes Film Festival. Young also recently starred in the limited series adaptation of Stephen King’s “The Stand” at CBS All Access (now Paramount Plus).

She is repped by CAA, Echo Lake Entertainment, and Shanahan Management.

“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.