Officer John Cooper returns to duty after recovering from back surgery and meets his new partner, Officer Jessica Tang, a tough and disciplined cop with her own set of baggage from working the streets. Lydia, whose new partner is Ruben Robinson, can't seem to escape helping a former CI who won't stay in safety. Ben, Sammy and Dewey chase an armed man into an elementary school, while Ben bumps heads with an intense street cop whose cynical attitude is affecting their work有些人注定只是过客，而有些过客，却会在心中留下永恒的印记。