Those ruby-red lips puffing away at a delicately hand-rolled cigarette, those shoulder blades jutting like weapons from a knockout of a backless, emerald-green gown — Keira Knightley would seem to be starring in an elegant period drama, one that’s predictably and self-consciously reserved.

“Atonement” is anything but. It changes again and again, lulling us in with its glamorous trappings before turning sexy, suspenseful, richly romantic and achingly sad. And if you haven’t read the Ian McEwan best-selling novel that inspired it, you’ll be dazzled by its twist of an ending.

Joe Wright, who directed Knightley to an Academy Award nomination for 2005’s “Pride & Prejudice,” rejoins most of his technical team from that film for this decades-spanning story of jealousy, betrayal, damage and repentance. Where his Jane Austen adaptation reveled in the gritty reality of the time, here he luxuriates in high style — everything has a shimmering, dreamlike sheen about it, perhaps as an homage to the sweeping, historical romances of long ago but without lapsing into parody. It’s just exceptionally well-crafted.

Screenwriter Christopher Hampton, an Oscar winner for “Dangerous Liaisons,” circles back on a few crucial moments as “Atonement” gathers its initial steam, a subtle, insightful reminder that perspective is everything. And the score from Dario Marianelli contains a clever mix of typewriter clicks and dings which gain momentum as the film’s young, aspiring novelist sets the key events in motion.

Knightley stars as Cecelia Tallis, an idly rich recent college graduate who indulges in a passionate encounter with Robbie Turner (James McAvoy), the charming and educated son of the family’s housekeeper, on the sultriest day of the summer in 1935 England. Cecelia’s younger sister, Briony (played startlingly as a child by the wide-eyed Saoirse Ronan), who has a schoolgirl crush on Robbie, catches them in the act and accuses him of a crime he didn’t commit, which changes the course of all of their lives.

(Without a bit of nudity, Wright has created one of the steamier sex scenes you’re likely to see, simply through a skillful use of breathing, lighting, silence and intimate camera angles. Knightley, no longer a girl playing a pirate’s game, finally feels like a woman in this role; McAvoy, meanwhile, has bulked up and gotten all hunky, a striking comparison to the lanky underdogs he’s portrayed in “The Last King of Scotland” and “Starter for 10.”)

Briony clearly has an affection for fiction from the beginning, writing plays and trying to coax her bored cousins to perform in them. But sheltered and just 13, she doesn’t realize the power her words can have, and the accusation she hurls at Robbie, born of pettiness, shock and envy, shakes up the family’s comfortable existence.

Skipping ahead in time, Robbie ends up in the Army during World War II and is among the British awaiting evacuation from the beach at Dunkirk. Slowly losing his grip on reality, he longs for a return to normalcy, to the woman he still loves.

And this is where Wright has staged his duly acclaimed, virtuoso tracking shot, a single Steadicam take that lasts an awesome 5 1/2 minutes. Following Robbie and a couple of other men as they trudge along the sand, it encompasses all manner of chaos in one fell swoop: arriving boats, dying soldiers, a slowly churning Ferris wheel, a melancholy choir, blood and carnage, destruction and loss.

Too show-offy? Perhaps. But it’ll leave you holding your breath, wondering how much longer it can possibly go on, how much more Wright can possibly cram in.

Cecelia, meanwhile, has decided to make herself useful, serving as a nurse in London and living in a spare flat. Never losing faith in Robbie, she dreams of the day he’ll come back to her. Briony, now 18 and played by Romola Garai, also has become a nurse — her attempt at making things right — but she and her older sister remain estranged.

Garai doesn’t have quite the disarming screen presence of Ronan, but then again she’s playing Briony as a young woman who’s been tempered by the gravity of her mistake. At the end, Vanessa Redgrave steps heartbreakingly into the role as an established novelist in the present day, looking back at her life from the brink of death. All three actresses are seamlessly tied together, though, by their clothing and demeanor, by the lost look in their eyes.

It’s one of the many great examples of attention to detail in a film that manages to be exceedingly careful while brimming with unabashed emotion.

“Atonement,” a Focus Features release, is rated R for disturbing war images, language and some sexuality. Running time: 123 minutes. Three and a half stars out of four.