Bruce Robertson is a detective sergeant serving in Edinburgh's "Lothian Constabulary". Robertson is a Machiavellian, intensely misanthropic man who spends his time indulging in cocaine and alcohol abuse, sexually abusive relationships, compulsive gorging on junk food, and, most of all, his penchant for "the games" – Bruce's euphemism for the myriad foul plots he hatches directed at workmates. He is able to pander to all of his vices during his annual holidays in Amsterdam. The novel begins by introducing the murder of Efan Wurie, a case Bruce has been assigned. The plot has little to do with the actual crime; instead, the novel traces Bruce throughout his life, told in a first-person, stream-of-consciousness style. Through narrative devices such as the tapeworm he acquires, the reader explores the facets of Bruce's personality and learns about his past, as well as the various tedious police routines Bruce absconds from, his often-backfiring sexual endeavours, and his various short- and long-term schemes and plots against his colleagues. Apart from the general malevolent scheming, along the way Bruce Robertson also seeks to satisfy his cravings for violence, drugs, sex, and pornography whilst happily voicing his racism, anti-Catholicsectarianism, and misogyny, all the while pining for his ex-wife. As the novel progresses, Bruce's mental health begins to deteriorate; it is revealed that he suffers from drug addiction and bipolar disorder, which, along with his inability to form meaningful, trust-based relationships, are exacerbated by latent, unresolved psychological problems caused by childhood abuses. Eventually Bruce is forced into taking leave due to injuries he suffers while dressed as his ex-wife, leading to the revelation that he committed the racially motivated murder that serves as the novel's main plot and that the colleagues he despises – particularly his boss Robert Toal – have been aware of his guilt all along and have been protecting him from the consequences of his actions out of a mixture of loyalty and pity. At the end of the story, Bruce kills himself, with his last thoughts being regret and hoping that his daughter does not know of his suicide.
Robert Toal: Bruce's workplace superior; held in contempt by Bruce, who nevertheless must attempt to curry his favour to win a promotion.
Peter Inglis: Another co-worker of Bruce, whom he suspects of being gay.
Amanda Drummond: A third co-worker of Bruce's, and the only one who openly disapproves of his behaviour and lifestyle.
Others
Carole – Bruce's ex-wife.
Stacey – Bruce's young daughter.
Clifford Blades: Registrar General for Scotland's Office, a member of Bruce's masonic lodge; a neurotic, insecure man, Clifford's marriage problems form one of the novel's major subplots.
Bunty Blades: Cliff Blades' wife and target of Bruce's dubious affections.
Shirley – Carole's sister and Bruce's sister-in law.
Rhona – Bruce's childhood girlfriend, in which the history of said relationship is revealed not by Bruce, but the tapeworm.
Plot devices
Language
Welsh's style of writing involves mainly Scottish English; but incorporates elements and loans from the Scots language, mainly the Edinburgh dialectal form. Also, Bruce uses rhyming slang, a common element of urban Scots dialects.
Themes
In Filth, Welsh deals with freemasonry, drug abuse, sexism, racism/sectarianism, pornography, prostitution and alcohol abuse, among other problems faced by the Scottish working class.
Carole
Carole, Bruce's ex-wife and the mother of his child, Stacey, is a device Welsh uses to reflect an outsider's view of Bruce Robertson's character; certain chapters only involve Carole's inner monologue related to Bruce.
The Tapeworm
At a certain point in the book, the narrative starts to be interrupted by a tube-like structure that appears on top of the text, and at first is only made of the word "eat" being repeated amid the zeros that fill the empty space within the tube. It is later revealed that this is actually the thoughts of the tapeworm growing inside Bruce's intestines. At first, the tapeworm only encourages Bruce to eat. Later, after becoming self-aware, the tapeworm starts to ask basic existential questions and names Bruce as "The Host". It also stumbles upon the existence of other worms. The tapeworm's monologues, which grow lengthier and more eloquent as the novel progresses, explain Bruce's backstory and how he became the person presented to the reader.
Film adaptation
A film adaptation of Filth was released on 27 September 2013. It is directed by Jon S. Baird, from a script he also wrote.
