The Duchess is a soap opera about the glamorous and scandalous lives of the rich and famous–though 200 years later almost no one remembers these particular celebrities.
17-year-old Georgiana Spencer (Keira Knightley) marries the rich and powerful Duke of Devonshire (Ralph Fiennes) but the marriage proves a disappointment. The Duke is cold and distant man who cares only about her ability to give him a son. Georgiana consoles herself with a glamorous lifestyle of fashion, parties, gambling and dabbling in Whig politics. Nevertheless she is devastated when her husband starts an affair with her best friend Bess Foster (Hayley Atwell).
Clearly we are supposed to feel sorry for poor Georgiana, though it is hard to shed too many tears for someone who led a life of such luxury at a time when most of her compatriots existed in what today would be considered Third World squalor.
The most interesting character is actually the villain of the piece, William Cavendish, the 6th Duke of Devonshire. Though a poor excuse for a husband, he was a leading supported of the Whig Party, the main reform movement of the period, advocating causes like the abolition of slavery and universal suffrage. The movie portrays him as stiff and awkward, honorable by his own lights and the standards of the day, but capable of casual cruelty. Frustratingly we are never really allowed to see inside his head.
In particular it is never explained why the Duke was apparently able to form a close and loving relationship with Bess, but never had one with Georgiana. It is hard to avoid some uncharitable speculation. Could it be, perhaps, that Georgiana was really pretty shallow, while Bess was not?