Politically ambitious new LAPD captain David Aceveda tries to crack corruption in the Barn by recruiting Terry Crowley to help him take down fellow detective Vic Mackey, leader of a police Strike Team consisting of himself, Shane Vendrell, Curtis "Lem" Lemansky, and Ronnie Gardocki. Meanwhile, detectives Dutch Wagenbach and Claudette Wyms investigate a woman's murder only to discover her missing daughter has been sold off by her addict father to a child molester.

In a routine sweep to nab every outstanding suspect, the detectives divvy up the warrants. But when they cast their nets, they bring up far bigger fish than expected.

When the body of a young hooker is found in the district, Dutch and Claudette get the full resources of the Barn for 24 hours and the help of the FBI to search for Dutch's serial killer.

Vic assists Connie as she tries to quit crack cold-turkey in a desperate attempt to keep her son, leaving Shane and Lem to investigate a strip-club mugging ring. Meanwhile, Dutch follows his instincts on the serial killer case and Danny is bitten by an HIV-infected perpetrator.

David works with Vic and the Strike Team to take down a dealer giving heroin to school kids, while Dutch and Claudette help a woman find her Alzheimer addled mother.

Detectives Wagenbach, Mackey and Wyms investigate a massacre at a women's shelter, and Captain Aceveda works with Lowe on the case of a stolen bicycle.

Flashback to the first day of the barn. Under pressure to get results, Vic and his new Strike Team make an impression on the streets. Dutch and Claudette realize they make a good team, and David discovers he doesn't have as much power as he thought he would.