San Diego's top homicide cop, world-weary Det. Sgt. Tommy Donahoo (Manila Time, 1995, etc.), heads south--to Tijuana, where the Mexican police say they need help solving the brutal rape/murder of Deedee Hernandez, socialite wife of a doctor with big-time connections. Was Deedee killed because of her do-gooder efforts to publicize the plight of thousands of ``dump people'' living on mounds of garbage? And have the town's evil forces (led by a monster known as ``Diablo'') managed to frame another decent activist, on Pedro Juarez, for the crime? So it seems--as Donahoo and his naive sidekick, rookie investigator Cruz Marino, are repeatedly doused in the cesspool of Tijuana's prisons, brothels, and bars. But, eventually, after more bodies surface and Donahoo gets alternately roughed up and sweet-talked (by a beautiful Tijuana lawyer with lips that ``pouted like little cocktail sausages''), it becomes clear that Donahoo and Marino aren't supposed to solve anything: They're being programmed to get so angry about the local horrors that they turn into ruthless vigilantes. Overheated, far-fetched corruption-melodrama, with more gross- outs than absolutely necessary--but readers who don't flinch easily will find steady interest in the darkly comic dialogue, unblinkingly grim reportage, and intriguing character tidbits.