Collins' adventures for one-armed N.Y. shamus Dan Fortune (Freak, Act of Fear, etc.) usually balance somber, brooding themes with taut action. This new case, however, is a bit too heavy on mood and message, a bit too light (despite a high body-count) on narrative propulsion. Jeanne-Marie Johnson, 20, an ambitious half-American refugee from Vietnam, is shot to death in an alley on Manhattan's rough West Side--soon after leaving her adoptive American family, the blue-collar Carters, on Long Island. Then young Roy Carter (whose older brother died in Vietnam) kills the drug-and-sex merchant whom he holds responsible for Jeanne-Marie's death. So the Carters hire narrator Dan to find and defuse fugitive Roy--who seems to be on a manic quest for vigilante justice, now hunting down one of the country's super-big drug/sex tycoons. . .while being stalked himself by swinish hit men. Dan follows Roy's bloody trail to California, along the way learning more about the young man's motives--only half--persuasive--for terrorism. (""Call him one more victim of Vietnam."") He also figures out exactly what happened to Jeanne-Marie, rehashes the thin yet gnarled plot at frequent intervals, and has a brief affair--notwithstanding a huge generation-gap--with Roy's ex-girlfriend. Despite a few sturdy vignettes in the old Collins manner: talky, repetitious, and portentous--with nearly all the drama taking place offstage or in the past.