Irvine Welsh's work is no stranger to the silver screen. His modern classic novel, Trainspotting, was also a success in its 1996 film incarnation. With Filth, a novel that came out in 1998, Welsh gets a similar psychedelic slant from writer-director Jon S. Baird. Following the debauched existence of police official Bruce Robertson (James McAvoy), Filth shows us the depths of depravity as only this Scottish scribe can.
Robertson's main obsessions in life are his wife, Carole (Shauna Macdonald), getting a promotion at work, and playing what he refers to as "the games," which basically just means fucking with his co-workers and only friend, Clifford Blades (Eddie Marsan). His latest attempts at psychological warfare involve undermining those within the constabulary who he views as a potential threat to his promotion and prank calling Clifford's wife, Bunty (Shirley Henderson, who isn't given nearly enough starring roles).
Amid this drama, the racially motivated murder of a Japanese student has taken precedence at the constabulary, leading Robertson to aggressively pursue potential leads while still finding time to make his co-worker, Peter Inglis (Emun Elliott), appear homosexual to the other members of the force (which he probably is). Incidentally, only from an Irvine Welsh character would you hear the phrase "Pussy's for faggots."
Robertson's drug-addled mindset continues to intensify as the film progresses. Hallucinating all manner of hybrid animals and therapy sessions with a cartoonish analyist (the always disturbing Jim Broadbent), we soon come to realize just how unstable Robertson is (cross-dressing is a factor). We come to question if his account of events was ever even real, or an utter delusion. And, speaking of delusions, Robertson also finds it necessary to give Clifford a little dash of ecstasy in his drink while they're in Amsterdam together. Not really sure what the Scottish obsession with "Sandstorm" by Darude is (if you've seen Under the Skin and have an ear for background music, you'll understand), but apparently doing drugs is the perfect excuse to play it.
Naturally, in the literary version, things end up slightly more macabre--with Robertson turning out to be the one who murdered the Japanese student. But perhaps casting James McAvoy made Baird feel like Robertson was too pretty to perform such ugliness on others, finding it necessary for him to perform it, instead, on himself.