Attention all aspiring writer and directors: do not, under any circumstances, adapt a novel with an unreliable first-person narrator. It rarely works; and if for some reason you do want to give it a try, please use the source material as a loose guide, and resist the urge to strategically hit certain major plot points, because important setup material will be lost – especially when it comes to a character’s back story. You can throw in all the voice-over you want, and you can present scenes from the perspective of the protagonist, but it will be pointless if you do not provide enough evidence for the protagonist’s outlook.
In regard to Jon S. Baird’s Filth, the film is a complete and utter failure both as an adaptation and as a stand-alone film. Adapted from an Irvine Welsh novel of the same name, Filth will be a frustrating watch for those familiar with the book, and a confusing watch for those coming in fresh. This is not to say it is completely without merit: there are a few sequences that work, and James McAvoy is more than convincing as a corrupt, vice-driven, piece of shit cop. Overall, though, the film is lacking in depth, intelligence, and characterization. To put it another way: Filth is no Bad Lieutenant. Baird goes for awkwardness and emotional highs and lows, but without any ties to reality Filth is all style and no substance.
The plot, which begins with a racially motivated murder, follows Detective Bruce Robertson (McAvoy) as he attempts to solve the case while simultaneously trying to fuck over all of his colleagues on his way to a promotion. Robertson’s method is characterized by his intense need to indulge in every vice imaginable — including the sexual assault of a 16 year old — all in the name of being manly and badass; a sensibility that the film not only fails to critique but at some points even promotes. Early on, though, we discover that Robertson’s hyper machismo is actually a facade meant to hide the fact that he is a lonely and sick man, driven by the ghosts of his past. However, instead of playing up Robertson’s back story, Baird elects to focus on juvenile laughs and inconsequential plot points. So instead of thoroughly exploring why Robertson plays games with people, Baird bombards us with supposed comedy by making us sit through increasingly stupid and un-witty moments of debauchery, with much of the intended humor being wildly misogynistic, homophobic, and racist.
Now, in a first-person novel like Filth, you can get away with this kind of ignorance because information is being filtered through the narrator’s consciousness (though there are still plenty of critics of Welsh’s politics). In a film, not so much; not unless you strictly adhere to a formula where the protagonist’s viewpoint is always dominant. In Filth there is a scene where Robertson is not present, and therefore the perspective is that of the camera’s (a sequence at the end involving someone watching a video recorded by Robertson) and the attempt at a first-person perspective is lost. Of course, the scene could be from Robertson’s imagination, but the film never gives any hint that this is the case.
Also, in regard to the hateful aspects of Robertson’s personality, there is a major plot point that is supposed to remind us that Robertson is simply putting on a persona, but in hindsight it feels like cheat. Without spoiling anything, I’ll simply say that there is a twist that is supposed to absolve Robertson of being a bigot and an asshole, but it feels opportunistic because it is not properly set up. In fact, nothing is set up in Filth. Instead of really paring down the approach and focusing on a tight character-driven story, Baird shoots for the moon with a maximized, overly-stylized attempt at black comedy; when what he should have done was draw inspiration from films like the aforementioned Bad Lieutenant, or Martin McDonagh’s In Bruges, a film that expertly juggles comedy and tragedy while presenting multi-layered characters and motivations.
To be fair, in some ways, it is understandable what Baird wanted to do. The novel is over-the-top and crazy — for starters, there is a talking tape worm — but Welsh took the time to flesh out his protagonist, thus placing the humor within a particular context. In the film version, Baird is far too concerned with presenting as much debauchery as possible. He goes for balls-to-the-wall energy, yet forgets to address the obvious: making the audience care. The problem is that Robertson is not developed, so watching him continually snort cocaine, or jerk off in a bathroom stall, or fuck someone’s wife, is not insightful or funny – nor is it filth; it’s crap.
— Griffin Bell