When an arrest reveals that drugs contaminated with a deadly bacteria have hit the street, the squad rushes to control the situation; Marlo reveals a shocking secret; Dov suspects Chloe of hiding secrets.

A robbery on a casino-bound bus filled with seniors threatens Frank and Noelle's wedding; Traci loses Noelle; Andy and Nick share an intimate moment.

Following violent, targeted attacks on 15 Division, the officers must piece together a past crime in order to find Oliver; the shooter's plan is revealed.