Following Dov's discovery of Chris's cocaine problem, Chris seems to have gotten on the right track. He's going to meetings, he's clean as a whistle—and he sure as hell doesn't need a babysitter. But while working a residential home invasion case, Dov discovers that Chris might not be ready to change after all. Back at the station, Steve lets Traci know that he is about to raid an illegal poker house where her ex, Dex, is a regular. With Traci's custody battle heating up, she knows Dex's arrest would end it once and for all; but does she really want Leo's father to end up in prison?

With a car-bomber still on the loose, the officers of 15 Division work frantically to track down the suspect while trying to figure out if more bombs have been planted around the city. Just when it feels like the worst is over, a bomb goes off in the evidence room of the station - with Andy McNally inside. But the violence - and the surprises - aren't over, leaving Sam Swarek dumbfounded.

The officers of 15 Division have been assigned a thankless task: "helping" tenants move out of a condemned subsidized-housing complex and into a neighboring building. While checking on an empty unit, Andy and Chloe find a man who has been tortured and beaten unconscious, leading to the discovery of a ruthless criminal operation. Meanwhile, Nick and Gail arrest a pair of teenage siblings with secrets of their own, forcing Nick to divulge some of the darker truths of his own past.

Following Dov's discovery of Chris's cocaine problem, Chris seems to have gotten back on the right track. But while working a residential home invasion case, Dov realizes that Chris might not be ready to change after all. Meanwhile, back at the station, Steve informs Traci that he's about to raid an illegal gambling den where her ex-husband is a regular. Both Traci and Dov must make decisions that will greatly affect the people closest to them.

Despite a generous offer from Inspector John Jarvis, Oliver isn't interested in extending his contract as Acting Staff Sergeant. He's thrilled to be going back to the street. But Oliver's day takes a serious turn for the worse when his daughter Izzy shows up unannounced at the station, and when he learns Professional Standards is arriving early for Duncan's dismissal hearing. Oliver and Andy do some crash-course prep, but both are rendered speechless when Duncan presents incriminating new evidence against Andy. Cornered, Oliver finds himself making the exact kind of professional deal he never thought he would be capable of making.

After the grim discovery of a missing man's body in the trunk of his car, 15 Division must try to find out what happened to Brian Gowdy - a high school teacher with no apparent enemies. While trying to track down their prime suspect, Andy and Sam go on the road to interview a list of prison inmates, leading them to someone with a surprising connection to Sam. Meanwhile, back at 15 Division, Traci leads the investigation and realizes they may have the wrong suspect.

After tracking a handgun found at a frat house brawl, 15 Division decides to go undercover at the club-land bar that's supplying the illegal handguns. During the undercover operation, Dov can't help but notice Chris's jumpy, nervous behavior - and when Chris goes to extreme lengths to ensure a specific drug dealer walks away without charge, Dov is left wondering just what exactly is going on with his friend. Meanwhile, Andy is devastated to learn that allegations made by her flamed-out rookie, Duncan, means she has to sit out the night's activities. Andy offers to help Sam with his missing person's case, which then takes a dark and unfortunate turn.

Andy worries that her rookie, Duncan, may not have what it takes to succeed on the job. But her fears get pushed aside when they discover a man found shot in a stairwell at a dodgy apartment building - leading to the discovery of an executed gang leader in a nearby apartment. Now, it's all hands on deck at 15 Division to stop a potential gang war from breaking out. Andy and Duncan find themselves alone with the one witness who can tie the killers to the crime, and in a life-and-death moment with a 12-year old witness, Andy may regret giving her rookie so many chances. Meanwhile, Gail follows up on another victim of the tenement shootings - a woman that took a stray bullet in the laundry room - only to make a harrowing discovery that will shake Gail to her core.

On the agenda for the day is 'Project Accountability' - a citywide operation to seize all "proceeds of crime" - then get to Fite Nite. The officers of 15 Division are assigned to seize items purchased with money earned illegally - a task no one is excited about. Andy and Nick are sent to an illegal gambling house - which turns out to still be in operation - and they dutifully arrest the homeowner. But after a confession that seems too good to be true, Andy recruits Sam to help her get to the bottom of what's really going on.

In the wake of Frank Best's dismissal, Inspector Jarvis promotes a reluctant Oliver to Acting Staff Sergeant. Today is also the day 15 Division gets a new rookie, Duncan Moore—an infuriating, eager, and connected millennial. Andy is up for the challenge and convinces Oliver to make her Duncan's Training Officer. But she may have acted too quickly… When Andy and Duncan end up as the first responders on a messy downtown homicide at a pawnshop, Andy has to try to show Duncan the ropes, while preventing him from compromising the case, himself, and his fellow officers.

In the wake of Frank Best's dismissal, Inspector Jarvis promotes a reluctant Oliver to Acting Staff Sergeant. Today is also the day 15 Division gets a new rookie, Duncan Moore - an infuriating, eager, and connected millennial. Andy is up for the challenge and convinces Oliver to make her Duncan's Training Officer. But she may have acted too quickly. When Andy and Duncan end up as the first responders on a messy downtown homicide at a pawnshop, Andy has to try to show Duncan the ropes, while preventing him from compromising the case, himself, and his fellow officers. Meanwhile, Sam's sister, Sarah, is ready to leave his bedside, but not until she gives Andy some harsh and cautionary words about what to expect in the long run with Sam.