The life and times of Jimmy ""The Weasel"" Fratianno, the highest-ranking Cosa Nostra member ever to turn government informer--in the nonfiction-novel mode, by a veteran mobwatcher. Working from extensive taped interviews, Demaris chronicles Fratianno's 40-year criminal career, from smalltime bookmaking in Cleveland's Little Italy to a stint as acting boss of the Los Angeles family: a short history of the underworld, with a cast of thousands. Fratianno ran into just about everyone--among the mob (Siegel, Lansky, Roselli, Giancana), in politics (Alioto), and in show biz (Ol' Blue Eyes, whom Fratianno got into the Knights of Malta). Still, though street-smart, he comes across as a loser: when he fell from grace and the organization put a contract out on him, after decades of hustling he could put his hands on only a hundred grand in assets. So he went to the Feds. Demarts knows the underworld scene and has done his homework, but Fratianno's world seems almost more tedious than treacherous--interminable dialogues about how this guy got whacked, how so-and-so whacked that guy in Detroit back in 1951, who should get whacked next unless he straightens out. . . . Pluses: some fine gang-who-couldn't-shoot-straight vignettes (the innumerable attempts to ""clip"" Mickey Cohen) and Demaris' perfect ear for thugspeak (""Listen, cocksucker, let me tell you something, you fucking prick. Why're you calling this Markovics a fucking con-man? Do you know what the fuck you're talking about, you motherfucker?""). Minuses: there are over 400 pages of thugspeak; background information on most characters is scanted or dropped into a one-line appendix reference; and Demaris' pure slice-of-life approach fails to illuminate whatever dark spirit drove Fratianno. Numbing and, except for Mafia freaks and Strike Force people, not worth the effort.