Chicago special-unit cops talk shop in a sure-footed sequel to What Cops Know (1990). While Fletcher (Journalism/Loyola Univ.) earlier covered the well-mapped territory of homicide, organized crime, etc., here she ventures into ``terra incognita''--the domain of the cops who work the Chicago special units of Bomb and Arson; Hostage/Barricaded/Terrorist; Crime Scene Investigation; Vice Control Section, Prostitution Unit; and Major Accident Investigation. As before, her family passport (her sister is a Windy City cop)--as well as trust earned by the first book--garners her access denied most writers, with these ``notoriously tight- lipped cops'' bending her ear with their troubles and tricks of the trade. Fletcher covers one unit per chapter, with each represented by eight or so officers, from street cops to lieutenants, who speak anonymously in short takes well-meshed for continuity and maximum drama. The talk is frank, informative (``You get into a tunnel vision thing when you get to a scene,'' one bomb-squad cop says), and full of rare detail (``Static electricity is the great danger in approaching a bomb,'' adds another, who explains that ``you can set a bomb off just by...having too much nylon on your body''). We learn that arson-squad cops wear steel-plated boots because ``when wood burns, it leaves the nails exposed''; that the majority of street walkers are ``gumps,'' or transvestites; that if a hostage- taker needs a phone to speak to the cops with, they'll provide one- -a Princess phone with a ``SMILE--HAVE A NICE DAY'' sticker on it; and that the ``Job'' is a tough, sometimes cruel career choice--and that not one cop Fletcher speaks to regrets having made it. Without the in-depth intensity of David Simon's Homicide (p. 527) and the confessional candor of Mark Baker's Cops (1985)--but, still, engaging, sometimes enthralling dispatches from behind the shield: a true-crime treat.