故事将承接第2季末，洛根·罗伊被他叛逆的儿子肯德尔伏击，为了确保家族、政治和金融联盟的安全，一场激烈的企业斗争有可能演变成一场家庭内战……
The detectives investigate a multiple homicide at a fast food restaurant; an addict gives his baby daughter to a drug dealer as collateral on an overdue loan; Internal Affairs reopens the Kirkendall case.
In the fourth season of this award-winning show, the action at New York City's 15th Precinct is as hectic as ever. While Lieutenant Fancy continues as precinct commander, Detective Andy Sipowicz, although still a bit rough around the edges, has mellowed with the birth of his son. Detective Bobby Simone and Detective Diane Russell take the next step in their relationship, James Martinez becomes the Squad Delegate, and Greg Meadavoy considers becoming a surrogate father. But one thing that hasn't changed is the squad's determination to make sure the bad guys get their day in court and to also attempt to maintain a touch of normalcy in their personal lives even as they investigate cases that often put them directly in the line of fire.
