“Downton Abbey,” airing as part of “Masterpiece Classic,” begins its fifth season Sunday on PBS.

It’s been a long, fallow wait for those who relish spending an hour a week on the rolling estate in the English countryside, but on Sunday it’s finally over. “Downton Abbey’’ returns for its fifth season on PBS as part of “Masterpiece Classic.’’

This season is as rich and nuanced as the others, and following the premiere, there’s “The Manners of Downton Abbey: A Masterpiece Special,’’ hosted by the series’ historical advisor.

It’s 1924 and the two worlds — upstairs where the gentry wear elaborate clothes, have serious talks and fabulous parties, and downstairs where the staff works incredibly hard so all of the upstairs events can happen — continue to become more complicated.

This season, the character to watch is Anna Bates (Joanne Froggatt). The quiet, unassuming woman who was thrilled to become Lady Mary’s (Michelle Dockery) maid, had earlier married Mr. Bates, Lord Grantham’s valet. A visiting footman had raped Anna. Later, he was mysteriously killed. All of that plants Anna in the middle of this season’s drama.

She suspects her husband killed the rapist, but they do not discuss such nastiness.

``Her and Bates are trying,’’ Froggatt says. ``They have moments of peace. They are not lying to each other as such, but keeping things from each other for their own sake. It is very touching, very moving.’’

``I love her,’’ Froggatt says of the sweet Anna. ``How can you not? She is good and lovely. I fell in love with her in about three scenes. She is who you want as a best friend. She is strong. She does not bow down to anyone. It takes a lot of strength to be a good person and not follow.’’

As Tom Branson (Allen Leech) proves. He began on the series as a driver and mechanic then married Lady Sybil who died in childbirth. A genuine, good, independent soul, he’s faced with tough choices this season. Should Tom stay to manage Downton Abbey with Lady Mary and raise his daughter in the privileged environs or start a new life in America?

``Tom has had a huge arc, if you think about it,’’ Leech says. ``He’s come from humble beginnings as a chauffeur to a firebrand politically, to his wife dying and then through the mourning process and now he is trying to find his feet again. He is now an estate manager and father to Sybbie and son-in-law to Robert and Cora and he has to find out what he wants.’’

The series, which airs first in the U.K., is often the subject of rumors, including how long it will last and who will be killed.

``As long as Julian (Fellowes, the creator) wants it to go,’’ Dockery says. ``It will go.’’

``Downton Abbey,’’ airing as part of ``Masterpiece Classic,’’ begins its fifth season Sunday on PBS (check local listings).