Season 4

Nick and Andy go missing while working under cover to infiltrate a meth pipeline; Swarek and the other officers find themselves in the middle of a rescue operation; Andy works to deal with all the change going on around her.

On her first day back, Andy is forced to work a bank robbery case with newly promoted Swarek; a distraught woman gives Nick perspective on his life with Gail; a bombshell is dropped on Noelle.

Andy and Officer Cruz butt heads when a disturbed woman forces them to make a crucial decision; an armed burglar is sought after a string of ATM robberies; Dov and Chloe have to work together.

During a routine traffic stop, Gail and Andy find a teenage boy bound and gagged in the trunk of a car; Oliver, Chris and Swarek track a gunman.

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.

When the investigation of a missing girl is linked to a past case, Detective Luke Callaghan comes back to help with search; Traci realizes she needs to get past Jerry's death; Sam and Andy face their past.

When a missing persons case is reopened, Swarek teams with his training officer to solve it; Chloe and Dov deal with a witch and her client.

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.

The squad searches for Chris' son Christian after he is kidnapped.

A routine drug bust turns into Traci's first murder case; Swarek, Oliver, Chris and Dov spend a weekend at Oliver's cabin; Andy and Sam both have confessions to make.

Andy finds out Marlo has been carrying out an unauthorized investigation into a pedophile; the drug sweep Traci is overseeing takes an unexpected turn when Sam leaves to help Marlo.

When Andy and Chloe respond to a routine 911 call, they are blindsided by an unseen shooter out for revenge.

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.