It's 1774 and the Duke of Devonshire (RALPH FIENNES) is looking for a wife who will produce him a male heir, and he's set his sights on teenager Georgiana (KEIRA KNIGHTLEY), daughter of Lady Spencer (CHARLOTTE RAMPLING). The young woman eagerly accepts his proposal, easily forgoing her attraction to young, aspiring politician Charles Grey (DOMINIC COOPER).
Quickly married, the Duke wastes no time in trying to father a child, while Georgiana just as speedily settles into her prominent role, spending time with politicians such as Charles Fox (SIMON McBURNEY) and theater types such as playwright Richard Sheridan (AIDAN McARDLE).
It isn't long, however, before she learns of her husband's adulterous ways, including that he has a daughter by a servant who's since died, meaning it's now up to Georgiana to be her mother. Things become more complicated when Georgiana convinces the Duke to allow Bess Foster (HAYLEY ATWELL) to stay with him. She's a married mother whose husband has absconded with their children and she's now homeless. She and Georgiana become fast friends, that is, until the Duke sets his sights on her as well.
From that point on, and as she fails to produce a male heir for the increasingly impatient and adulterous Duke, Georgiana must contend with the related indignities of their marriage, as well as her growing attraction to Grey who's reentered her life.