Another ex-cop writes a novel--and in this overlong but impeccably authentic law-vs.-terrorists procedural, former NYPD captain Mahoney, like Joseph Wambaugh, Robert Daley, et al., shows why a pen, as well as a gun and a badge, are standard police equipment. Mahoney's hero is nothing new: He's a generic maverick NYPD detective, Brian McKenna, whose antics have gotten him exiled to Brooklyn. What is fresh is the author's astonishingly tight, almost minute-by-minute detailing of the five-day case that returns McKenna to the ``Bright Lights'' (Manhattan). The cop's break comes when he notes a suspicious character and trails him to a drug lair, where the cop kills the suspect in a shootout. That burst of violence, as it turns out, is the story's last until the final pages--a great rarity for a cop novel, but McKenna's intense focus on the nuts-and-bolts of detection and on bureaucratic cop-intrigue keeps the narrative energy pumping, albeit fitfully. Taped to the dead man's back are a severed finger and a photo of the amputee- -clues to a kidnapping, figures McKenna, who uses this discovery, plus his friendship with the chief of detectives, to lever onto Manhattan's Major Case Squad. Recognizing the amputee's shirt as a Brooks Brothers, the cop i.d.s the man as a rich Peruvian, while other clues point to the kidnappers as members of Peru's Shining Path guerrilla group. Piece by difficult piece, McKenna and his squad--fencing with brass and the obligatorily incompetent FBI agent, and using subterfuge, surveillance, phone taps, high-tech cameras, etc.--home in on the kidnappers' Spanish Harlem den. In a tense and moving conclusion, the cops raid the hideout--with the avowal, in order to prevent further kidnappings, to take no prisoners.... Short on action but very long on insider's savvy: a strong bet for patient police-procedural fans.