In the Royal movie sweepstakes, the Windsors win decisively over the Spencers, with Helen Mirren’s Elizabeth II easily besting Keira Knightley’s Georgiana Cavendish. While Stephen Frears’ “The Queen” was an insightful, clever dissection of the political relationship between the current monarch and Tony Blair in the aftermath of Princess Diana’s death, “The Duchess,” Saul Dibb’s adaptation of Amanda Foreman’s book “Georgiana, Duchess of Devonshire,” is just a handsomely appointed but lugubrious period soap opera centered on one of the distant ancestors of the so-called “People’s Princess.”

The costume piece begins in 1774 with young Georgiana Spencer being married off to the older William Cavendish, Duke of Devonshire (Ralph Fiennes) by her status-conscious mother (Charlotte Rampling). Her major responsibility, the emotionally chilly nobleman stiffly informs her, is to provide him with a male heir. But another is to serve as a maternal substitute for a young girl whom he’s fathered by a now-deceased servant.

Unfortunately, the two children who issue from the union are both girls, though Georgiana does strike a chord with the Whig politicians her husband supports, particularly Charles Fox (Simon McBurney) and his handsome protégé Charles Grey (Dominic Cooper), as well as a society favorite who can draw crowds even to political speeches. On a vacation in Bath Georgiana befriends the straight-talking Bess Foster (Hayley Atwell), whose husband has run off with another woman, taking their boys with him, and even coaxes the Duke into letting the poor woman stay with them in London. That turns out to have been a mistake, though, as William becomes enamoured of Bess and the sons he retrieves for her, and Georgiana must tolerate another woman living with her and her husband in a single, admittedly large London house—with the duchess the real outsider in the arrangement. She ultimately looks elsewhere for affection, finding it in an affair with Grey that ends with her having to make a choice between scandal and love, or compromise and her other children.

Presumably we’re supposed to take the peculiar threesome of the duke, the duchess and Mrs. Foster as an eighteenth-century analogue to the twentieth-century misfortunes of the current Prince of Wales, his beautiful and popular young wife, and the woman he always truly loved, who happened to be first married and then divorced, and thus in either case unacceptable as a royal partner. But such a comparison would make the smoldering affair between Georgiana and Grey, as well as the duke’s physical mistreatment of his wife, rather tacky at the very least. On the other hand, setting it aside leaves the tale little more than a soapy story of a couple of failed marriages and infidelity among the posh and pampered, with a side order of the self-denying lengths to which mothers will go to protect and nurture their children—all staples of what used to be called women’s pictures (not chick flicks, which are aimed at the under-fifty crowd).

It doesn’t help that the film is afflicted with a bad case of “Barry Lyndon” syndrome. Dibb appears to be enamoured of the Kubrick film (understandably, given that it’s a masterpiece), but he was ill advised to try to mimic its style and tone, and even many of its narrative elements (gambling parties, drawing-room confrontations). The grave intensity of Kubrick’s treatment of Thackeray seems merely static and wooden here, with the painterly compositions (like William’s standing motionless at a window, looking out on the children playing) coming across as affectations rather than means of making an artistic point. In many respects this does feel like what the earlier film was often wrongly called—a coffee-table movie.

Knightley, to be sure, tries to add a modern touch to the proceedings, occasionally curling up her face into a pout rather than remaining the emotionless mannequin, but in only a few cases does she really come alive as a character (as in a moment that adds some sudden energy to the proceedings, when her drunken stumbling sends her crashing into an ornate candle stand, setting her wig afire). Fiennes, by contrast, holds himself in—one can hardly imagine a greater contrast to his performance in “In Bruges”—and winds up resembling the late Nigel Hawthorne in one of his less showy roles. Atwell can do little with the enigmatic Foster, whose motives and feelings remain opaque throughout, nor Rampling with Lady Spencer, who’s little more than a coldly ambitious dowager. And while McBurney provides a few nice moments channeling Simon Callow as Fox, Cooper is a bland bit of beefcake as Grey.

Of course, one can always get by admiring the accoutrements—Michael Carlin’s production design, Karen Wakenfield’s art direction, Rebecca Alleway’s sets, Michael O’Connor’s costumes and the widescreen cinematography by Gyula Pados that sets them all off in a glossy, often hazy glow. But whoever was responsible for the hair styling went overboard—Knightley’s big do’s sometimes resemble those of Princess Amidala rather than the Duchess of Devonshire (perhaps they should be credited to the special effects team). And Rachel Portman’s score is unhappily generic.

Mention of Fiennes’ resemblance to Hawthorne calls to mind one more point. There’s little sense of historical context in “The Duchess.” Apart from perfunctory allusions to the American and French Revolutions, there’s little sense of the events that were at the center of Hawthorne’s great triumph, “The Madness of King George.” A bit more of that might have given more depth to the movie and made it seem less an example of skating over the surface of the lives of characters who themselves, here at least, are portrayed as doing little more than skating over the surface of history.