"Let us not become weary in doing good, for at the proper time we will reap a harvest if we do not give up." (Galatians 6:9)

How often do you choose to do the right thing? Sometimes it's easy: handing back money when you've been undercharged; helping someone to carry a bag, cross the street or de-ice their window. Sometimes though, it's a little more difficult and costly, like stopping to leave your insurance details on the windscreen of the car you just dinked, or smuggling a memory stick belonging to a Russian informant to MI6 in an effort to save his family from execution.

While that last example won't be familiar to many of us, it does happen to be the basic setup of Our Kind of Traitor, the taut British espionage thriller opening this week. It sees Ewan McGregor cast as a man who finds himself in the wrong place at the wrong time, and who can't stop himself from doing right in response. McGregor is Perry, a university professor who is on holiday in Morocco with his wife Gail (the fabulous Naomie Harris), desperately trying to repair a marriage that he's wounded with an affair. While there, they develop a strange and instant relationship with Dima (Stellan Skarsgård), a banker for the Russian mafia who knows too much and believes his family are about to be targetted. His only hope is to recruit a man of integrity who'll take his information directly to British Intelligence, and in Perry, he thinks he's found one.

His faith is well placed, as Perry makes the first of many decisions which place personal integrity above personal safety. He takes Dima's memory stick of information to MI6 agent Hector (Damian Lewis), but can't avoid being drawn into the ensuing intrigue, and a host of dangerous situations to boot.

With its range of exotic locations, glamorous characters and regular-guy-turns-spy plot, it can be viewed as something of a companion piece to the BBC's superb recent TV drama The Night Manager. Both are based on novels by master espionage author John le Carré; both centre around a few 'good' people trying to take down an unassailably powerful monster. However, while The Night Manager's central character Pine is driven by revenge, Perry is motivated by a desire to do good and make up for past mistakes; a sense of repentance, even.

Our Kind of Traitor isn't a perfect thriller – some of the plot twists can be seen coming several miles off, and the language is unnecessarily strong throughout – but it is a thoughtful and intelligent one. It's not afraid, much like last year's James Bond movie Spectre, to confront the idea of the evil behind evil; the larger financial forces which enable horrors like trafficking, blood diamonds and arms dealing to thrive unpunished. Yet it's also brave enough to believe that we can be better than that; a light that shines in the darkness and hasn't been overcome.

The key, on this grand canvas, and perhaps in the smaller examples of everyday life, is the sort of integrity displayed by Perry. Edmund Burke is credited with saying that "evil prevails when good men do nothing"; this story does a good job of illustrating that point. Sometimes it's easy to do good; sometimes it's much harder. The moment we grow weary of doing so, however, we betray the light that shines in even the darkest places.

Martin Saunders is a Contributing Editor for Christian Today and the Deputy CEO of Youthscape. You can follow him on Twitter: @martinsaunders