British costume dramas rarely survive the journey to Middle America, where the locals aren’t beholden to an aristocracy. But “Vanity Fair” is unusually accessible, because Indian-born director Mira Nair (“Monsoon Wedding”) strips away the fancy-pants pretensions of the ruling class with a deftly comic touch. Yet, in doing so, she’s also stripped the massive William Makepeace Thackeray novel of its complexity, reducing a caravan of social climbers to a Reese Witherspoon vehicle and forcing a famously cunning character to impersonate a heroine.

In a game approximation of an English accent, Witherspoon plays Becky Sharp, the orphaned daughter of a failed but talented artist in early-19th-century London. In the first scene, we get a glimpse of Becky’s gumption, as she extracts an inflated fee from the Marquis of Steyne (Gabriel Byrne), the one gent who’s willing to purchase her father’s work.

Becky is shipped to a boarding school, where she makes a lifelong friend in Amelia Sedley (Romola Garai) and acquires enough of the social graces to earn a job as a governess for the well-connected Pitt family. But she soon discovers that the elder Pitt (Bob Hoskins) is a degenerate and his family’s estate is a shambles.

When the resourceful Becky gives the household a semblance of good taste, she wins the favor of the family’s wealthy matriarch (Eileen Atkins) and the love of her ne’er-do-well nephew, Rawdon Crawley (James Purefoy). But the aunt’s avowed interest in unconventional couplings doesn’t extend to her own kin, and after she learns that Rawdon has married a mere governess, she disinherits him.

Meanwhile, Amelia has married the arrogant, impulsive George Osborne (Jonathan Rhys-Meyers), against the wishes of his family and the hopes of her more sincere suitor, William Dobbin (Rhys Ifans). After both husbands are summoned to fight against Napoleon’s army in Belgium, the two wives join the sizable contingent of support personnel who turn Brussels into an annex of the London social circuit.

When the Battle of Waterloo disrupts the festivities, the film finally applies its gravity to matters of life and death. But in the aftermath, the misfortunes that befall the two women are haphazardly dramatized, beginning with their glossed-over pregnancies and extending to their financial woes. In the novel, the stalwart Amelia is a counterpoint to the scheming Becky; in the movie, Amelia’s descent is a sketchy subplot in the near-beatification of Becky, who keeps the profligate Rawdon out of debtors’ prison with the help of the suspiciously generous marquis.

While Rawdon is doing heaven-knows-what, the marquis subsidizes Becky’s rise in high society, culminating in a musical performance for the king. The anachronistic dance number is reminiscent of “Moulin Rouge” and is one of several Indian-flavored embellishments that Nair adds to the story, to dazzling, if distracting, effect.

The director also has a pitiless eye for satirical details, as the vainglorious nobles are often seen peeling away their wigs and powders. So it’s disappointing that the same light of truth doesn’t shine on the main character. When the story jumps ahead a dozen years and finds Becky toiling in a German casino, we haven’t seen enough to know if this fallen woman is a victim of class comeuppance or her own connivance.

Notwithstanding the trimmed narrative, this version of “Vanity Fair” has a witty script, a rich look and an excellent cast surrounding the fearless and photogenic Witherspoon. It’s her star power that got the movie made and ensured that it would be distributed in the colonies, where few people will know or care that the original story was subtitled “A Novel Without Heroes.”