Given the spate of costume dramas that have hit the big screen recently, you could be forgiven for failing to distinguish one silk-clad heroine from another. And “The Duchess”—based on the biography of the same name by Amanda Foreman—does little to make the dazzling Georgiana of Devonshire stand out from the crowd.

Like “Marie Antoinette” and “The Other Boleyn Girl,” “The Duchess” is a period film about a beautiful, young, aristocratic female trapped in an unhappy situation.

This time, it’s a marriage with three people: Georgiana, her husband, and her husband’s live-in mistress. The Duchess Georgiana, played by Keira Knightley, consoles herself by taking a dashing young lover, flaunting the newest fashions, and schmaltzing her way to the top of London society.

The real-life Georgiana Cavendish was a relative of Princess Diana, a fact the filmmakers make sure to exploit. However, linking the story to Diana of Wales will not make this 18th century romp any more successful, nor will it evoke any more sympathy for its wronged society beauty than it would for anyone else in her beautifully jeweled silk shoes.

“The Duchess” has a lot working in its favor, including strong performances, visual delights, and a moving score. However, the movie as a whole is less than the sum of its parts. While it’s not expected for a period drama to be mind-blowingly original, it should have something that makes it at least appear different. Moments of “passion” and revelation in the movie are met with lines of dialogue that could have been taken straight out of a contemporary soap opera, with liberal dashes of 18th century language, of course. We are expected to sympathize with Georgiana, because, as she says, “All my life, I have been fighting my way upstream.” Such clichés are only met with others like it, including “The concept of freedom is an absolute,” which she delivers later.

It doesn’t help that this dialogue is held together by a very shaky and predictable plotline. At the beginning, there is an attempt to incorporate political commentary into a film based around societal intrigue–but as soon as it becomes intriguing, the story reverts back to the default quibbles of the aristocratic couple, and all goes downhill from there.

It’s not all pomp and circumstance, though. The acting is effective, with Keira Knightley putting in a memorable performance as Georgiana. Knightley successfully portrays the Duchess’s range of emotions from unhappiness at her three-person marriage to ecstasy in scenes involving her lover, Earl Grey. Ralph Fiennes, her philandering husband, gives a skilled performance as the selfish and inattentive Lord of Devonshire. He and Knightley make a convincingly unhappy couple onscreen. Even the aristocratic British accent—often hard to do well–is right on par.

Half the fun of watching the movie is seeing the lavishly overdone costumes. The sets ooze 18th century opulence. The dinner party scene—shown in the movie’s trailer—encapsulates the splendor enjoyed by 18th century British aristocrats with its bejeweled guests and ornately decorated interiors. The rustling skirts and gleaming chandeliers, however, can’t hide the truth—“The Duchess” is smoke, mirrors and frequently-insubstantial pageantry.

“The Duchess” isn’t meant to be a groundbreaking movie by any stretch of the imagination. Its aim is to entertain rather than to educate. But gorgeous dresses and champagne can’t mask the fact that stale dialogue and flat storylines will ruin a movie, whatever its aim may be. Director Dibb’s offering isn’t terrible—but it isn’t great either. If you want light entertainment and social scandal, an “OC” box set is likely to give you more satisfaction—if you can do without the powdered wigs.

—Staff writer Betsy L. Mead can be reached at emead@fas.harvard.edu.