A Jane Austen adaptation is always welcome—so long as it doesn’t involve zombies—but “Love & Friendship” proves especially engaging. Partially that’s because it represents a work that’s not been done as a film before—the early novella “Lady Susan,” probably written around 1794 but not published until long after the author’s death. (It appears under a title borrowed from another of Austen’s juvenilia.) But mostly it’s because the story of a manipulative eighteenth-century widow arranging good matches for both her daughter and herself has been so winningly, and wittily, brought to the screen by writer-director Whit Stillman and a superbly chosen cast.

Stillman is known for the verbal sophistication of his films, which have been all too rare, but until now they’ve been situated in modern settings. This one proves that his style is perfectly attuned to the late eighteenth century, when the book was written, and especially to imagination of the young Austen. This isn’t a slavish adaptation: though characters frequently compose and read letters, Austen’s epistolary format can’t be simply transferred to the screen, and the book’s unfinished character necessitated imaginative sprucing and finessing. The marvel is that the result is so finely gauged that most viewers will find it difficult, if not impossible, to discern where Austen stops and Stillman begins; some of the best lines are hers, but others are his. Rarely has the fit between author and adapter felt so marvelously right.

Kate Beckinsale is the lady in question, whom we meet as she departs the stately home that she, as an impecunious widow, has lately visited, leaving furious women and despondent men in her wake. Looking for a logical place to stay, she and her devoted attendant make their way to the rural estate of Churchill, to spend time with her accommodating brother Charles (Justin Edwards) and his wife Catherine (Emma Greenwell), who welcomes Susan with appropriate gentility but is deeply suspicious of her plans, which—in asides that are very helpful to us—she shares with her confidant, the equally duplicitous Alicia Johnson (Chloe Sevigny), here transformed into an American with a very perceptive husband (Stephen Fry).

Catherine’s concerns are validated when her shrewd guest casts her net for Catherine’s visiting brother Reginald De Courcy (Xavier Samuel), a handsome young fellow who falls for her charms even though his sister—along with his mother (Jemma Redgrave) and father (James Fleet)—express deep concerns about a possible union between them. But their intervention is hardly decisive; what shatters the smooth operation of Lady Susan’s plan is the sudden arrival of her daughter Frederica (Morfydd Clark), who’s been expelled from her exclusive boarding school. Everyone seems to take an interest in the lovely, shy, and eminently marriageable Frederica’s future, including Reginald.

That leads her mother to invite to Churchill Stillman’s most inspired addition to the assemblage there, Sir James Martin, alluded to only indirectly in the book but here embodied to hilarious perfection by Tom Bennett. Martin is exquisitely dense and utterly oblivious of his own imbecility; his idiotic remarks leave all around him—save the endlessly tolerant Charles—standing in stupefied silence as he grins shamelessly in their direction. He even transforms some dinner conversation involving a plateful of peas into the most amusing cinematic treatment of that vegetable since James Mason and Christopher Plummer dealt with the subject in “Murder by Decree.”

If Bennett makes an unparalleled stooge, however, he certainly doesn’t steal the movie so long as the deliciously haughty Beckinsale is around. Dropping a stream of icily mordant observations with only the slightest arch of an eyebrow, she dominates the picture while leaving space for the fine supporting cast to shine even in her shadow. Samuel casts an especially fine figure as Reginald, but Edwards isn’t far behind as eager-to-please Charles, and Clark, Sevigny, Greenwell, Fleet and Redgrave all have their moments. The sole regret is that Fry, who seems born to this Austen-Stillman world, gets little more than a cameo.

Shot mostly on Irish locations, “Love and Friendship” (a title borrowed from another of Austen’s early works) was clearly made on a limited budget, but the period detail in the physical production is nevertheless highly satisfying. Anna Rackard’s production design, Louise Mathews’ art direction and Eimer Ni Mhaoldomhnaugh’s costumes are all top-drawer, and Richard von Oosterhout’s cinematography gives appropriate luster to the compositions. The images are beautifully complemented by Benjamin Esdraffo and Mark Suozzo’s subtle score, which makes way for as well-chosen a parade of classical snippets as the one Kubrick selected for “Barry Lyndon.”

“Love & Friendship” will appeal to Austenites, of course, but anyone who appreciates a sophisticated, witty comedy of manners should seek it out. You won’t be disappointed.