Filth

There's a thin line between cops and criminals in Filth, a contentiously graphic, darkly comic novel by Irvine Welsh, the author of Trainspotting. Corrupt Det. Sgt. Bruce Robertson of the Edinburgh police is up for a major promotion — if he can just curb his bent for cocaine, booze, and sex — to solve a vicious, racially motivated murder. Seething beneath it all is his gradual descent into madness, which is editorialized upon by a tenacious talking tapeworm that he can't seem to purge. Welsh excels at making his trash-spewing bluecoat peculiarly funny and vulnerable — and you will never think of the words ''Dame Judi Dench'' in the same way ever again. A-