Downton Abbey's Christmas Christmas Special episode will focus on Teapot Dome Scandal and how it affects the Royals and the Crawley family.

The episode, set in the late spring and summer season, has Rose's 'coming out' wherein she is presented at Buckingham Palace. The infamous Teapot scandal interweaves the lives of the Crawley family and the Royals, while Robert goes to "great lengths" to protect his family and the royals.

Shirley MacLaine will continue in her role as Cora's mother Martha Levinson, who arrives from America with her playboy son Harold, played by guest star Paul Giamatti, who has had a recent standoff with law.

Lady Mary's two admirers Tom Cullen and Julian Ovenden from the last season return this season to play the rest of their parts. Tom Cullen plays Lord Anthony Gillingham, an old childhood friend of Mary whom she had not seen in years, while Julian Ovenden will be back as the aristocrat Charles Blake.

In the special episode, light shines on the old Isobel when even she discovers that she has an admirer. Ethel struggles with a "moral dilemma" while Daisy gets an "unexpected visitor" and Carson treats the staff on a fun day out.

The two-hour episode will be shown on ITV on Christmas Day at 8.30pm. The cast from the fourth series will be returning with Dame Maggie Smith as Lady Violet, Hugh Bonneville as Robert, Michelle Dockery as Lady Mary Josephine, Joanne Froggatt as Anna and Brendan Coyle as John Bates.

Much-anticipated guest appearances will be James Fox as Lord Aysgarth, a member of high society, Guy Williams as King George V and Oliver Dimsdale as the Prince of Wales.

Basildon Park in Berkshire will serve as the Crawleys' London residence, while Lancaster House will stand as Buckingham Palace. Other parts of the episode were shot at Goldsmith's College and West Wittering beach in Sussex.

The Season Four finale was viewed by 10.5 million people out of which 40 per cent was British audience, according to the Telegraph.

Guinness World Records recognised the programme as the most critically acclaimed English-language television series of 2011, the year it earned 27 nominations for Primetime Emmy Awards.

Downtown Abbey
Downton Abbey cast members at the 19th annual Screen Actors Guild Awards in Los Angeles, California January 27, 2013. (Reuters)