The opening of the film Captive, based on a true story, shows a man in the possession of evil. At one point Brian Nichols, who has just murdered four people, seriously injured a fifth and taken a young mother and drug addict hostage, claims there is a "demon" inside him. British actor David Oyelowo plays this unlikeable protagonist with chilling authenticity. Nichols is clearly very bad and very dangerous, and God does not seem much in evidence in the terrible murders he perpetrates as he breaks out of jail, fleeing a sentence on a rape charge.

God also does not seem much in evidence in the life of meth addict Ashley Smith, played by Kate Mara, who is struggling to get clean at a 12-step recovery group meeting. She cannot get past the first step, never mind the other 11. She has already lost custody of her daughter and is on the verge of losing everything else. It is only when Nichols takes her hostage that she finally takes first step with its crucial admission of powerlessness and unmanageability. He holds a gun to her head and threatens to shoot her if she does not take more of the drug, and in front of our eyes we see her finally reach acceptance and from that, the courage to change.

This is one of the pivots around which the plot of Captive revolves. The second is the part played by God in recovery, both from evil and from addiction. There is a big debate taking place in the US and the UK at present about the "higher power" among members of 12-step recovery programmes such as Alcoholics Anonymous and whether it is possible to overcome addiction to alcohol or anything else without God.

Rick Warren's best-selling book The Purpose Driven Life is central to the plot of Captive and Warren even shows up in person, in some real-time footage of him and the original Ashley on Oprah, at the end of the movie.

No 12-step organisation explicitly recommends his book. In Captive, Ashley is handed it after a meeting, and promptly chucks it in the bin. The woman who gave it to her sees this, retrieves it and then posts it to her. So Ashley finally begins to read it and this is what enable her to take the second and third steps of recovery - she comes to believe a power greater than herself could restore her to sanity, and makes a decision to turn her will and her life over to God as she understands Him. This leads to the redemption of both Ashley and in a sense, Brian Nichols.

It is a powerful story, beautifully told, even if the emphasis on Warren's book could have been a little more subtle. Captive will be a great teaching tool, for churches and faith schools in particular. It also contains strong, broader mass market appeal. Addiction, violence and random incidents of good and bad luck are not far from anyone's life today, if they ever were. Oyelowo drives his character to the heart of all of this.

He was inspired to make the film by the power of the story. "There was something so incredible about how these two people's lives intersected on this given day, both on a clear downward spiral. He had murdered four people in that day. She was a meth addict who had lost custody of her own daughter. These two people who are thrown together by complete coincidence. She had only moved into that apartment the day before."

He was sent the script four years ago. He had read The Purpose Driven Life, and loved the way the script seemed to articulate its message that God's purpose for our lives is so much greater than the ones we see for ourselves, he explained. "I couldn't think of a better illustration of that than this meth addict who went on to live an amazing life beyond being taken hostage."

Brought up in a Baptist church, at 16 Oyelowo himself asked the question that led to a personal encounter with Jesus. His parents were churchgoers. "I very much piggy backed on their faith. It didn't really mean much to me and it wasn't until I was 16 that I kind of struck this very naive deal with God, whoever he was, and said, 'Look, if you don't become real for me, I'm out.' And within three months of making the mistake of asking, He went, 'Oh ok, here I am.' And so that was kind of it."

He has this much in common with Ashley Smith, who had been raised in the church but was not living out any faith when Nichols arrived at her house.

"She actually said that at the moment when Brian Nichols, at gunpoint, told her to take meth with him, she felt Christ take over Brian's body and say, 'Choose life or death. Which is it?' And in some ways she attributes her salvation to, partly anyway, Brian Nichols and him invading her apartment that day. Christ was definitely at work and that's why she's now living the life she's leading."

Like most people, he has suffered in ways that lead to feelings of anger and loss. There were things he could and had to latch on to in order to play the character. "But I thankfully have not experienced anything remotely like what you see in the film." One of the reasons Brian was tipped over the edge to his violent escape from jail, leaving a trail of death behind him, was learning he had a baby son. The resulting desperation to see him, just as he was facing 25 years in jail, sent him on his murderous rampage. "Without excusing Brian at all for what he did... I do have four children. The thought of not being near them is something I can't abide," said Oyelowo.

He does not know whether Nichols is a Christian but he is in touch with his mother, and she told him only two weeks ago that Nichols, serving life with no chance of parole, is repentant and feels he is where he needs to be. "I'm not shy personally about talking about my faith," he said. He discovered through his mother that Nichols had been very moved by some of the things about Christianity that Oyeloyo has shared. "I don't know where he's at spiritually, but I do know that he looks on this event with real regret and repentance."

He is conscious of the recent controversies around police shootings of black men in the US.

"Black men have been killed by police for far, far less than what Brian Nichols did that day. I think partly why Brian Nichols wasn't gunned down that day was because Ashley Smith had been let go by him. One of the reasons that black men are being killed, sometimes indiscriminately, in America is because there is a perception, there is a prejudice, there is a preconception that they are criminalised by virtue of the colour of their skin. So as a knee jerk reaction they are shot, out of fear. Whereas just a shred of humanity that he was able to demonstrate in terms of letting her go, I think, was partly what was playing on those cops' minds."

Oyelowo has himself experience of what can only be described as discrimination. Employment of black and ethnic minority actors in the UK is a controversial subject. There have been many complaints about unnecessary shortage of roles. Oyelowo, born and brought up in the UK, did not go into details but said: "I live in America, I work in America, there are reasons why that is the case."

His work there has brought him great success, most notably his stunning performance as Martin Luther King Jr in Selma. He said: "I know for a fact that roles like Dr King in Selma or even being able to produce a film like Captive would not be what I would be doing if I still lived here. I love living here, I love the UK, I loved working here, but my ambitions weren't fully able to be realised here. So I think there is a lack of willingness to see these kinds of stories told. The ironic thing is, when you gain a little bit of success elsewhere, you can come back and do those stories you couldn't get told while you were here. And so that's sort of the next step for me."

One of his early roles was with the Royal Shakespeare Company in Ben Jonson's Volpone. Shakespeare could put so much into one line, one character, he said, and believes Captive has something of this. "It's intimate, it's largely about two people, but it speaks to much bigger themes: spirituality, the dynamic between a man and a woman, race, crime, murder, rape. It's all in there, all of what you would find in a Shakespeare play. But as with Shakespeare, it is the juxtaposition of the little and the large. That's what Captive also has."

He believes God was in the end at work on that day. "The role of God, the effect of God and the power of God is love as far as I can see. And so that in my experience just never fails."

Faith resources about Captive are available at www.ethosmedia.org/captive