From 1996 through 2014 Charles Campisi headed NYPD's Internal Affairs Bureau, working under four police commissioners and gaining a reputation as hard-nosed and incorruptible. When he retired, only one man on the 36,000-member force had served longer. During Campisi's IAB tenure, the number of New Yorkers shot, wounded, or killed by cops every year declined by ninety percent, and the number of cops failing integrity tests shrank to an equally startling low. But to achieve those exemplary results, Campisi had to triple IAB's staff, hire the very best detectives, and put the word out that bad apples wouldn't be tolerated. While early pages of Campisi's account bring us into the real world of cops, showing, for example, the agony that every cop suffers when he fires his gun, later pages spotlight a harrowing series of investigations that tested IAB's capacities, forcing detectives to go undercover against cops who were themselves undercover, to hunt down criminals posing as cops, and to break through the 'blue wall of silence' to verify rare--but sometimes very real--cases of police brutality.