Northern Ireland in the 1980s was, well, troubled. It follows, therefore, that any film that attempts to portray the Troubles should be gritty, slightly unnerving and morally complex, 'Fifty Dead Men Walking' leaves you feeling harrowed, so I guess it fits the bill.

'Inspired by' ? and this certainly leaves a great deal of room for reinterpretation ? the autobiographical novel of the same name written by Martin McGartland and Nicholas Davies, writer/director Kari Skogland has produced a film which certainly feels authentic.

It feels unpolished, understated, un-Hollywood. The accents are thick; the horror is stark but simple; the actors look like everyday folk; and everything seems just a little bit dirty, tatty and decrepit. Most importantly, there is an over-riding and all-pervasive sense of hopelessness (and pointlessness) that must, surely, have been prevalent in Belfast at the time.

Martin Mc Gartland (Jim Sturgess) is a cocky young Catholic man who dabbles in petty crime. He gets by selling stolen clothes and perfumes; has very few concerns; and even fewer allegiances. Because of his illicit behaviour, the British 'peacekeeping' force is mildly interested in him. After a tussle with the police, the Irish Republican Army (IRA) also takes some notice.

More for the cash it'll get him, than a strong ideological bent, Martin begins working for the IRA. British Special Branch agent Fergus (Ben Kingsley), who pounces on the opportunity of infiltrating the IRA, tries to persuade Martin to act as a double agent.

Martin grapples briefly with the moral (and potentially fatal) implications of betrayal, but the IRA's indiscriminate killing of 'innocent' people soon pushes him in the direction of Fergus. Having betrayed the IRA, however, his fate is pretty much sealed: excruciating torture and a bullet to the head.

Unless, of course, Fergus can protect him.

Sturgess's Martin is so likeable that it is hard not to rally behind him, and while both the IRA and the British Army are portrayed negatively, the Brits do come across as the lesser of two evils. So, we have a hero. A man who, at great personal cost, indirectly saved the lives of at least 50 other men with his snitching ways.

Just don't think about it too much. Because if you do, our hero starts looking a little morally reprehensible; a little self-centred.

And, whether or not that was the intention, it certainly leaves you feeling, well, troubled.

Click here to watch the 'On Screen' review of the film!