Atonement tells the story of two lovers whose potential for luxurious bliss in 1930s Great Britain will be destroyed by a startling, horrendous lie and torn by war. The premise may sound like just another throwback to the historical epics of the 1940s but it is to the great credit of the movie, based on the rich novel by Ian McEwan, that it places equal gravity on that third person who tells the lie that separates the two lovers. By the end, we will see all three of their lives transformed and left mired in despair and longing for missed opportunities caused by an act of spoiled immaturity.

The movie opens in a posh, rich mansion in London where we see the Tallis family daughters, Cecilia (Keira Knightley) and 13-year-old, Briony (Saoirse Ronan) who bask under the shining sun in the summer of 1935. Cecilia tries to deny it, but the attraction between her and Robbie Turner (James McAvoy), the son of the housekeeper, Grace (Brenda Blethyn), is strong and irresistible. Briony, who is already regarded by her parents as a blossoming writer, has a crush on him, too, as she glimpses in jealousy and miscomprehension a romantic flirtation that builds between Cecilia and Robbie.

One day Briony walks in on Cecilia and Robbie in the throes of carnal passion in the library and misconstrues it as him attacking Cecilia after earlier intercepting a lewd letter that he mistakenly sent out as a love letter to her sister. Thus, after she comes across the seeming rape of one of her cousins, Lola (Juno Temple), her seething envy and misperception of Robbie as rudely coming on to her sister combine to compel her to falsely accuse Robbie of the crime despite that she never clearly saw the real perpetrator. This false testimony’s repercussions spill over into World War II after Robbie decides to serve in the military after four years in prison and is assigned as one of the British soldiers to fight in France.

The film, directed by Joe Wright and adapted by Christopher Hampton, makes the shrewd choice to stay faithful to the distinctive three-act storytelling structure of the original novel while enhancing it with some modern touches of filmmaking in a few scenes. Briony’s clear remove from the true grasp of the situation, for example, is magnified from the first act’s omniscient point of view in the novel by showing the two key moments – the flirtation at the fountain and the library tryst – first from her perspective and then at ground level with Cecilia and Robbie. The second act, set four years later, flips through different time points among Robbie’s struggle to stay alive and sane in the midst of the war, Cecilia’s efforts to keep her love alive with him by exchanging letters, and the nurse training of Briony (now played by Romola Garai) who is guilt-ridden for her grave, childish mistake.