Fans will remember that the third season brought big changes for the cast. Detective Lydia Adams had to adjust to life with a new partner, a new potential love interest and some drama with her former partner, Russ.
Officer John Cooper continued to struggle with his addiction to painkillers, which started to seriously interfere with the job. It also turned the tables with his rookie partner Officer Ben Sherman who has now moved on to bigger things on the force.
And then there was the season's most shocking storyline, with Detective Sammy Bryant, played by Shawn Hatosy, losing his partner Nate Moretta in the line of duty.
In the season premiere, John returns to work after recuperating from back surgery and meeting his no-nonsense new partner, Jessica Tang (played by new cast member, Lucy Liu). Elsewhere, Lydia also gets a new partner; an armed man is pursued into an elementary school; and Ben tangles with a cynical street cop.
Southland S4 Starts on Thu 19 Jul at 21:30