He is a Cambridge-educated housekeeper's son who falls for Cecilia Tallis (Keira Knightley), the eldest daughter of the upstairs household, then is wrongly accused of a misdeed by Cecilia's imaginative younger sister, Briony (initially played by Saoirse Ronan).
The film is split into three time periods, the first set during one balmy summer's day and night in 1935 at the Tallis' Gosford Park-like estate, the second between war-torn London, where Robbie and Cecilia are briefly reunited, then occupied France with Robbie, one of thousands of British troops trying to reach Dunkirk and safety.
The film is both epic and intimate.
Yeah, it's quite an intimate epic. I was with Joe the other night and it's the first time he's used that term and I thought, "That describes it better than anything we've called it in the last year and a half."
In terms of human experience, it is on an epic scale, but the narrative is quite simple. It's about two people who love each other, something really bad happens to them, and then we watch the repercussions for them and the person who committed the crime.
The irony being that the book was supposedly "unfilmable."
Strange that. I think those perceived flaws or perceived difficulties, all those jumps in time, back and forth, seeing the same scene three times from three different points of view, have turned out to be some of its greatest strengths. I can see why people said that, but they were wrong, I think.
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When you first read the script, what struck you about Robbie?
His goodness; his lack of conflict. I didn't really recognize him as a member of society. I thought he was a little bit too good, too bold, too complete and too undamaged. As an actor, I've always used conflict for every character I've played and there was none there and that terrified me.
It wasn't until I accepted the reality of that, that someone like that might exist, that I started being able to play the character properly. It took me a little while in rehearsals to bed that down and get over my desire to make him have an edge or be interesting from the inside out, instead of otherwise.
Robbie isn't the central character in McEwan's novel but is clearly the beating heart of Wright's film.
He is the easiest character to sympathize with, I think. One of the reasons that storytelling exists is because we need to see ourselves represented, and go, "Wow, aren't we wonderful, aren't we funny, aren't we interesting, aren't we pathetic, look at us being torn apart."
It's always more interesting to an audience to watch a really good person being ripped to shreds. For that reason, they had to have somebody in there who is wholly good, because even Cecilia is a bit of a pain in the arse to begin with, and Saoirse playing Briony is a little terrifying demon.
The one character that goes all the way through it is the wee girl and because she's played by three different actresses and because she's scary, you can't really be her as an audience member, whereas you can be Robbie because although he's slightly unrealistic in terms of his goodness and his almost angelic status, it's easier to go, "I could be that good and therefore that could be me."
There's been a lot of buzz surrounding "Atonement" since it opened the Venice Film Festival in August. You were a presenter at this year's Academy Awards. What would an Oscar nomination mean to you?
It would mean I would have a second opportunity to try and take in the Oscars because the last time was all a bit of a blur.
I'd come from Uganda that day. I was there doing charity work for the Red Cross. So that was really quite strange, spending days and nights with 50,000 people living in abject poverty and then you go to the Oscars.
But I would be chuffed, I would be thrilled, I would jump up and down on my bed. But if I don't get one and if the film doesn't get any, and Joe doesn't get any -- and I hope to God he does, and I hope Seamus McGarvey, the director of photography, does -- and if Keira doesn't get anything, I would hope we don't suddenly re-evaluate the piece of work we've performed in, that it is somehow not as good. I know how hard it is to make any film, never mind a good one that people want to go and see, and I'm exceptionally proud to be involved in this.
What would it mean for the film?
If the film got nominated in some of the more high-profile categories, I think it would mean a hell of a lot more money in America, which would be great. It's done really well money-wise [in the UK] but "The Last King of Scotland" was making nothing [in America] until Forest [Whitaker] got his Oscar and then bang, it made $20 million. So, hopefully, that will happen because it will inspire people to go out and see the film.