LONDON — It’s rare to find either dementia or older women featuring prominently in mainstream dramas. But in the new BBC film “Elizabeth Is Missing,” Glenda Jackson, 83, takes on her first screen role in 27 years as a woman facing the rapid erosion of her faculties, even as she searches for answers to mysteries in both the present and the past.

Since her return to acting in 2015, after 23 years as a member of Parliament for the Labour Party, Jackson, a two-time Academy Award winner, hasn’t shirked a challenge. In 2016, she played a unanimously lauded “King Lear” at the Old Vic in London; in 2018, she won a Tony Award for her role in Edward Albee’s “Three Tall Women” on Broadway, returning there this year to play Lear again. (Although Jackson’s performance earned glowing reviews, the new Broadway production did not.)

But she hasn’t undertaken a cinematic role since 1992, when she appeared in another television movie: Ken Russell’s “The Secret Life of Arnold Bax.”

“Elizabeth Is Missing,” which premiered on BBC One on Sunday, is based on a 2014 novel by Emma Healey. Jackson’s Maud lives a life peppered by Post-it notes reminding her to lock the door, to keep appointments, to drink coffee (“good for memory”). As her forgetfulness deepens into something worse, she becomes increasingly worried about her best friend, Elizabeth, who seems to have disappeared.