A-tone-ment, noun 1. Making amends for a horrible act or deed.

For some, this feat of reparation may never be realized. For Briony Tallis, this will be a lifelong lesson that she must teach herself to finally be free.

Atonement, based on the best-selling novel of the same name, tells the story of two sisters, 13-year-old Briony (Saoirse Ronan) and her determined older sibling Cecilia (Keira Knightley). During one unseasonably warm English summer, a feverish romance develops between Cecelia and the housekeeper’s son, Robbie (James McAvoy).

Before a family dinner, those feelings are finally acted upon and later consummated; unbeknownst to these lovers, Briony has been watching. Even worse, the young girl has also been carrying a torch for Robbie herself. When she makes her presence known, fear takes over.

Hell hath no fury like a tween scorned: Briony, still very immature – and to some – inexperienced, concocts a vengeful story implicating Robbie in a crime that he didn’t commit.

“[Briony] makes herself believe things,” says Ronan. “And after a while, she decides to go with her imagination and to believe herself instead of anyone else.”

This misunderstanding rips so many lives apart that Briony will spend the rest of her years seeking atonement for her deeds in the most creative way imaginable.

For Knightley, Atonement, re-teamed her with Pride & Prejudice director Joe Wright. That relationship proved undeniably successful the first time around; Knightley earned a Best Actress nod for her role as Elizabeth Bennet.

The same Oscar buzz has swirled around Atonement for both Knightley and her costar McAvoy. Atonement’s literary author espouses the virtues of the later, a gifted 28-year-old.

“There is a stamp of experience in the corners of his eyes,” says writer Ian McEwan. “Through James’ performance, you feel pathos.”

Knightley concurs, “He has the ability to completely morph into any character you give him.”

Even Wright had immeasurable praise to bestow upon his leading man: “I’d first seen James in a play about seven years ago, and I could tell how good he was. I’d offered him parts twice before, and this third time was the charm.

“James has working-class roots, and that was very important; Robbie’s story is that of a working-class boy whose life is often at the mercy of the snobbery of an upper-class family. James also has a deep soul and isn’t afraid to show it. The character is described by Ian McEwan as having ‘eyes of optimism, and James has those.’”

Given Atonement’s heavy subject matter, the mood on the set definitely springs to mind.

“We weren’t pissing ourselves laughing everyday,” says McAvoy.

But both he and Knightley do admit to a bit of fun during the shoot. Both stars are inarguably contemporary figures on the Hollywood and English scenes. For a young cast of film’s finest, friendship and bonding were a definite.

“We all stayed in the same house,” reminisces Knightley.

After long days of shooting, she, along with Romola Garai (who plays Briony as an older teen), and other actors like Benedict Cumberbatch (who starred with McAvoy in Starter for 10) and Juno Temple (daughter of director Julien Temple) – to name a few – let their hair down, engaging in revelry and drinking.

Since McAvoy’s character was an outsider, he had different accommodations, although Knightley jokes, “He still came around most nights.” McAvoy can next be seen in the fairy tale love story Penelope, costarring Christina Ricci. He’s quite earnest about his talent and loves playing characters that he feels are a bit “arrogant.”

“I get to show off a bit and act like the dog’s bollocks,” he remarks.

One of his favorite characters in his impressive career was Dr. Nicholas Garrigan in 2006’s The Last King of Scotland.

Knightley, is just happy to get a much-needed break over the holidays. The graceful actress confesses that she’s been “eating and sleeping” and loving every minute of it. She remains very open-hearted about working with a lot of the burgeoning film talent in both England and stateside.

She also kids around about her next major career move: “If you can find me a good science fiction script, I’ll do it!”

Atonement is currently in select theaters.