Director Saul Gibb lives out his vision of 18th century high society in The Duchess, a costume drama based on Amanda Foreman’s bestselling biography of socialite Georgiana Spencer Cavendish. The movie is more like an episode of Gossip Girl than an in-depth chronicle of British history, but it’s enjoyable enough if you’re more interested in the wigs than the Whigs.

Keira Knightley is Georgiana (G to her friends), a beautiful and charismatic socialite married off in 1774 to the powerful Fifth Duke of Devonshire (Ralph Fiennes). Only 16 years old, Georgiana enters into the marriage with naïve dreams of love and freedom that are quickly dispelled after an unpleasant wedding night. The much-older Duke wants only two things from his wife: loyalty and a male heir. Each of these proves harder to come by than he might have imagined.

As time goes on, the marriage devolves into a relationship that would today merit its own feature on The Maury Show. The Duke is the ultimate controlling husband. He scorns the daughters produced during his marriage, demands that Georgiana bring up his own illegitimate child, and takes Georgiana’s best friend Bess (Hayley Atwell) as his mistress, eventually inviting her to live with the couple in the palace and seating her as a third at their dinner table.

Georgiana, meanwhile, looks for self-expression in fashion and politics in order to deal with the constraints of her marriage. Striking up acquaintances with playwright Richard Sheridan (Aidan McCardle) and politician Charles Fox (Simon McBurney), she uses the fame she’s earned as a fashionista to draw attention to the Whig party and to champion the cause of the everyday man. Her political associations bring Georgiana into contact with future Prime Minister Charles Grey (Simon McBurney), a romantic interest as hot as the Earl Grey tea named after him. Sparks fly between Grey and Georgiana, and the film plays out as a drama of true love tragically stifled.

Powerful acting is the movie’s biggest strength. Keira Knightley has become a bigwig (pun intended) of UK costume dramas, and she draws from her own past experience as a fashion icon to embody the glamour of this historic celebrity. Knightley seems right at home in the elaborate silk gowns and tightly wound corsets that she wears throughout the film (the costume designers consulted paintings of Georgiana to recreate her look), and she floats through majestic country manors and beautifully decorated rooms with a graceful ease. Her performance is overshadowed by Ralph Fiennes, however, who gives a spin to the one-dimensional Duke written into the script. Fiennes vacillates between brutal recklessness and reflective regret to create a sympathetic villain, the kind that delivers his blows with a bowed head and a soft voice. The complex relationships between these characters are steered by Rachel Portman’s incredible music score, which ranks right up there with The Dark Knight’s as one of the great film scores of 2008.

Despite the inventiveness of the acting and the decorations, the story itself seems unsatisfying and unoriginal. Dibb chooses to focus the story entirely on Georgiana’s romantic and emotional life. Extravagantly long close-up shots chronicle every flicker of emotion passing through Keira Knightley’s face, but give the audience little in the way of perspective. Like Marie Antoinette and The Other Boleyn Girl, The Duchess is just another story of one woman’s struggle in the face of a patriarchal society. The main themes of sacrifice and freedom are unoriginal at best: No one is free and everyone makes sacrifices, we get it. Instead of focusing on romantic politics, the film could have focused more on what made Georgiana’s story unique. Apart from one drunken ballroom scene, little mention is made of G’s debaucheries: her drinking, drug-use, gambling and affairs with leading politicians. Not a word is said about the Duchess’ 1780 novel The Sylph, a critique of 18th-century high society. Her fascinating political accomplishments are glossed over, and there is little talk about the American Revolution that began only two years after Georgiana’s marriage. In short, Knightley plays a character whose personality and intrigues have been as tightly compressed as her corset. But it is Keira Knightley, and when all is said and done, let’s be honest: We know we love her.