"Enemies Within," by Matt Apuzzo and Adam Goldman Illustration by Matt Dorfman In the aftermath of 9/11, the New York Police Department began regarding Islamic "houses of worship - and everyone who prayed there - as possible criminal organizations," Matt Apuzzo and Adam Goldman tell us in "Enemies Within." For that reason, those houses of worship get special attention from officers in the department's intelligence unit. The "mosque crawlers," as the unit's paid informers and undercover agents are known, make "secret recordings of sermons," Apuzzo and Goldman write. David Cohen, the deputy commissioner for intelligence, compares such work to raking coals in a fire pit: "You might find a smoldering ember - a hot spot waiting to catch fire." However, unlike other accounts of New York's counterterrorism efforts, such as Christopher Dickey's "Securing the City" and Michael Sheehan's "Crush the Cell," "Enemies Within" does not glorify the work of the cops. Instead, it attempts to portray Cohen as a sinister force, a man who oversees a network of surveillance operations that tramples on civil liberties. Cohen's unit, which has a $60 million budget, is "a separate squad that operated in near secrecy and fancied itself a miniature C.I.A.," Apuzzo and Goldman write. During one eight-month period, the unit "opened at least 15 secret terrorism enterprise investigations." A former C.I.A. station chief in New York City, Cohen operates with little oversight. He "makes the rules." The two authors, both Associated Press reporters, build their narrative around the investigation of Najibullah Zazi, who planned to blow up the New York subways in 2009. Their account of the case, tracing Zazi's trip from Colorado to New York, is interwoven with potted histories of Islam, Al Qaeda and F.B.I. investigations. Zazi is tipped off about the investigation by someone who works for Cohen's unit. It's a rookie mistake, and a big one. The case is nearly blown. But the fallout is contained, and Zazi eventually pleads guilty to terrorism. Despite the authors" efforts to blacken Cohen and his unit, the squad does not come off all that badly. In this account, at least, they seem clownish but relatively harmless. The officers collect vast amounts of intelligence. Just as the East German Stasi was once overwhelmed by the amount of information it had gathered, so are the New York City police. After years of work, they end up not with a database of potential terrorists but with a collection of jumbled, useless notes. They mix up Sunni and Shiite. They seem to gravitate toward bakeries that have the best pastries. With these amusing if less-than-­shocking revelations, Apuzzo and Goldman attempt to build a case against Cohen and his unit. Some of it is less than persuasive. As it turns out, the good guys, which is to say those who find fault with Cohen, are ruggedly handsome. One, a deputy chief, is "tall and lean, with a short haircut to match his temper"; another, an F.B.I. agent, has "a strong jaw and a full head of dark hair." As for Apuzzo and Goldman's actual argument, it seems confused. At times, they suggest spying on people in mosques is wrong. At others, they find fault with the way the officers carry out the operations. One might conclude that if the police were better at record-keeping and stayed away from pastry shops, the squad would be O.K. That hardly seems to be the point of the book, given its concern with civil liberties. Apuzzo and Goldman fail to present sufficient evidence for either case - that the unit is hopelessly ineffective, undermining attempts to fight terrorists, or that it has inflicted lasting harm on Muslims, shopkeepers and others. "Enemies Within" breaks ground in its reporting, but the definitive account of the city's extraordinary and controversial counterterrorism program, one that lays out its importance as well as its problems, has yet to be written. Tara McKelvey, a frequent contributor to the Book Review, is a feature writer for BBC News and the author of "Monstering: Inside America's Policy of Secret Interrogations and Torture in the Terror War." An earlier version of this review included a sentence with a quotation from the book that was incorrectly applied in the review. The sentence read as follows: "Mosques are like "bug lights for aspiring jihadists," a New York City Police Department analyst says." As the book made clear, it was the radical Islamic Thinkers Society that the analyst likened to "bug lights for aspiring jihadists," not mosques.