Andy's world explodes by a seemingly senseless act of violence during a concert shooting. When she sets out to unravel the details, she comes into direct conflict with Luke's former partner, Detective Jo Rosati, a new detective with Division 15. As Rosati investigates the case, sparks soon fly between her and Luke.
Andy and Gail participate in a drug bust by going undercover as cocktail waitresses but things don't go smoothly. Traci finds herself drawn back to Detective Barber while a complaint is filed against Dov. Andy unintentionally speaks to Sam a little too freely and candidly about her relationship with Luke.
Strange happenings and a full moon rattle the rookies. Andy and Sam investigate the theft of some severed heads from a medical lab. A particular man catches their attention as a suspect with his obsessive behavior. While trying to protect a young woman who could be the next target, Andy puts her life and Luke's in jeopardy.
The torching of a Laundromat is the latest in a series of arsons which the 15th Division must work. The list of suspects is long so Chris and Gail take to the streets while Traci interrogates a person found at the scene. Andy is left to deal with the widow who insists on entering the burnt-out building which ends with the two of them trapped inside.
A local car dealership is the backdrop for a Division 15 sting operation to crack down on suspects with outstanding warrants. However, when one of the captured criminals tries to bargain for a lighter sentence by offering insider information to Dov and Chris, it puts them in peril in a booby-trapped meth house. Meanwhile, Jo convinces Luke to help her on a high-stakes surveillance job.
Indications are that the East Jameson gang was involved in the hug of a police informant, so solving the case will be difficult. The pressure is on when Superintendent Elaine Peck sets up at the station. Elsewhere, Andy is paired with Detective Rosati who unintentionally makes Andy privy to a secret that involves Luke.
Detectives Callahan and Rosati are at odds over how to correlate and interpret the facts of two vicious crimes. Luke feels strongly that the latest woman attacked on her watch is connected to an unsolved rookie's hug, but his erratic behavior gets him kicked off the case.
Gail and Traci apprehend a man who mysteriously collapses at the station which in turn places Division 15 under quarantine. Andy and Swarek are after a brutal bank robber and his partner but it will take some out-of-the-box thinking to solve this crime. Dov goes out on a first date with the bomb tech who saved his life.
Swarek takes Dov and Gail on a stakeout operation to prevent an Asian gang from committing hug. Mounted Unit training day has Andy and Chris taking part in a competitive horse training event as Andy makes an effort to move on with her personal life.
While working a kidnapping case, Andy and Swarek find themselves on the scene of a car accident. As Swarek and the rest of Division 15 pursue the kidnapper and missing child, Andy remains at the scene with a woman trapped in her car. A transgression involving Gail puts Chris at odds with Dov. Andy concludes that it's time to re-evaluate her life.
Andy, Dov and Traci participate in an undercover training exercise which results in some unplanned situations and choices. Chris and Gail must determine if a young boy found tied up is the result of bullying.
Gail's stolen uniform has the rookies looking for a cop impersonator, but it's Chris and Dov who find clues that may offer up the motive. While undercover, Swarek finds himself in a life threatening situation when he and Andy can't stay apart.
Swarek's gone missing and Andy tries to find clues that will help her and the rookies locate him before it's too late. Meanwhile, investigating this case will implicate one officer and threaten Andy's job.