LOS ANGELES — Acclaimed actress Glenda Jackson will launch the 50th season of PBS’ “Masterpiece” drama showcase next year.

The film “Elizabeth is Missing,” with Jackson as a woman in search of a vanished friend even as she copes with dementia, will air Jan. 3. It’s based on the Emma Healey novel of the same name.

Jackson, 84, is a two-time Oscar winner, for “Women in Love” and “A Touch of Class.”

“Masterpiece,” from WGBH Boston and among TV’s longest-running weekly prime-time series, has been home to award-winning shows including “Downton Abbey” and “Sherlock.”

The anniversary season also will include “All Creatures Great and Small,” a new seven-part series based on James Herriot’s books about his adventures as a veterinarian in 1930s England.

The series is set for a January debut. A 1970s adaptation of Herriot’s work was a public TV hit.