In Filth (W.W. Norton; $14), Irvine Welsh, author of Trainspotting, offers up another look at the ugly side of human existence. The hero is Bruce Robertson, a paranoid, sadistic, corrupt Edinburgh cop whose only redeeming quality is that he hates everyone with equal prejudice. This being a cop story, there’s a murder to solve, but that plot plays second fiddle to Robertson and his exploits, which involve a trip to Amsterdam, a great deal of angry sex and reckless drug use, and general terrorizing of the populace. Any enjoyment comes from witnessing Robertson’s suffering, be it from a rash in his nether regions, a parasite in his lower intestine, or just the misfortune life heaps upon him. This is Welsh’s strength: at once savoring life’s many little moments of misery and wallowing in them. Consequently, reading Filth becomes an act of vicarious sadomasochism.