Vic Mackey is the leader of an elite Strike Team unit, a group of cops effective at eliminating crime while operating under Vic's set of rules that sometimes cross the line between legal and illegal. The precinct's new captain doesn't like Vic's tactics, and wants to bust him off the force.

After a rocky start, Vic and Aceveda have formed an uneasy alliance that Claudette is determined to destroy. Vic's personal life is in shambles and a new nemesis on the street forces the Strike Team to risk everything in the pursuit of one last big score for their "retirement fund".

After scoring big with the money train, the Strike Team plays it cool to avoid arousing suspicion. Tensions are stretched further when Vic finds himself at odds with his team, but hostilities are quickly forgotten when Aceveda reveals that the team is the target of an Armenian mob hit.

The Strike Team has dissolved. Vic and Shane are assigned to regular detective duty, while Aceveda is leaving to begin his new job on the City Council. Although Vic often clashed with Aceveda, he quickly realizes that new captain Monica Rawling also has her own agenda.

As the Strike Team battles racial tensions in the city, friction inside the Barn escalates with the arrival of Jon Kavanaugh, a dogged Internal Affairs lieutenant obsessed with taking down Vic.

Vic and the Strike Team are distraught over Lem's death. After Vic learns from Claudette that the Chief plans to force him into early retirement, he vows to wreak bloody vengeance on Lem's killer before losing his badge, while Shane, overcome by guilt, becomes reckless and suicidal.

Pressured to take down Pezuela, Vic's skeletons finally come tumbling out of the closet as he faces threats from all directions—primarily from damaged protégé Shane.