It’s not often you come across a mainstream film that offers much meat to pick over on a scriptwriting level. Thrillers in particular seem to be honed with engineering precision, ensuring that thrills and spills are delivered in escalating fashion with meticulous timing. And characters do what characters do in such genre flicks: they’re taciturn but tenacious in their pursuit of justice, baddies are sinister to order, and if anyone swaps their white hat for a black one there’ll be some seeding before the transition takes place.

None of the above is a complaint by the way — I enjoy a well-tooled Hollywood thriller if it delivers the goods it promises. What, then, to make of Law Abiding Citizen? On the surface a piece of mainstream hokum, it presents a scriptwriting issue of considerable interest that you’d not expect from a straight genre movie, one that’s at the heart of the story.

We open on the grisly killing of a woman and her daughter in front of the eyes of Clyde Shelton, the man of the family, who is tied up and helpless to act. Then cut to the legal consequences of this, when slick prosecutor Nick Rice negotiates a deal meaning that while one of the culprits will be executed, the other will be out of prison in just a few years. All of this serves to position Nick as the antagonist in the relationship, and Clyde as the hero.

Jump ten years, and it’s not long before the positions are reversed. Clyde puts his considerable inventiveness and resources into bringing down not only the bad guys, but the legal team involved in the prosecution, and in fact the whole social edifice it rests on. Dude has issues. Grievance issues. And he can’t let go. Not even after sawing up one of the bad guys — an act he commits to put himself in prison, where he masterminds his Joker-style plan to hold a city to ransom with his increasingly bloody acts of vengeance.

All of which is nonsense of a high order, but nevertheless thoroughly enjoyable hokum if you’re in a mood to see stuff get all blowed up. It has the same kind of crazed appeal as the plan to install Rage Against The Machine’s obscenity-peppered polemic Killing in the Name Of as the Christmas number one to show The Man — in the form of Simon Cowell — what da kids really want. And Kurt Wimmer’s script has some fun with the ridiculousness of it all, little moments of humour softening the mayhem like slippers on a serial killer.

So, how to ensure that we turn against Clyde and sympathise with Nick? Part of the solution is in casting. Nick Rice is played by Jamie Foxx, a smooth dude for sure. And Clyde is played by Gerard Butler, in a conspicuously uncharismatic way. Make Clyde too likeable, even in his crazed plan for vengeance, and the scales would tip too far and the audience would get where he’s coming from when attempting to off the city’s leaders with napalm. And that won’t do: anarchy cannot reign, at least not for long and without consequence.

Conversely, Nick becomes more sympathetic as those around him are blown to smithereens. Particularly when he loses a promising young female colleague, we’re inclined to think that perhaps Clyde’s one man terror campaign is maybe a bit out of sorts. Which is a shame: there were hints of a more Fight Club style film in Law Abiding Citizen at times, but desire for sanity and the reassuring ker-ching of the box office cash till put paid to such commercially suicidal thoughts. Pity.