The Shield plants itself firmly post-third season but pre-fourth season. The fallout from the money train robbery has already taken place and Detective Vic Mackey and his strike team of dirty cops are on the verge of disbanding. The game begins with the final episode of the third season. Officials want the team reassigned, members of the team are unhappy with the way things are going and Captain Aceveda tells them it’s going to take a major bust to salvage any hope of keeping the team alive. The big bust in question turns out to be an arms race between the Byz-Lat and One-Niner gangs. Mackey is tasked with breaking up the battle, finding the guns, and arresting as many of the thugs in charge as possible.