Andy's world explodes when a fresh-faced university student is caught in the crossfire during a random concert shooting. Devastated by the seemingly senseless act of violence, she sets out to unravel the motive and track down the shooter -- putting her in direct conflict with Division 15's new detective, Jo Rosati. Meanwhile, as Rosati investigates her own angle on the concert mayhem, sparks fly between her and her former partner, Detective Luke Callaghan.
Everyone's living their "might-have-beens". Andy and Gail go undercover as cocktail waitresses to clean up a drug infested club, but get more than they bargained for when their fellow waitress turns out to be the girlfriend of a vicious criminal. Traci wrestles with feelings for her old flame Jerry; Dov and Chris are at odds when a complaint is made against Dov; and Andy opens up about her commitment to Luke
As a full moon hangs over the city, the rookies are unnerved by a series of strange occurrences. While investigating the theft of three severed heads from a medical lab, Andy and Swarek pick up the trail of a mentally unstable man who has stopped taking his medication. In an effort to protect the life of a young woman at risk, Andy exposes herself - and Luke - to potentially lethal consequences.
As 15 Division recovers from the shooting of Det. Luke Callaghan, a series of arson culminates in the torching of a laundromat - and the rookies are forced to confront their own burning issues. Chris and Gail take to the streets and encounter a man from Chris's past, while Traci interrogates a young firebug found at the arson scene. Meanwhile, when Andy tries to stop the grieving widow from entering the burnt-out laundromat, the two women are trapped in an unstable building with a burnt corpse and must rely on the Fire Department to cut them free from the debris.
Using a local car dealership, 15 Division runs a sting operation to crack down on suspects with outstanding warrants. One of the criminals they capture tries to bargain for a lighter sentence, by giving information that puts Dov and Chris in peril at a meth house. The discovery of a homeless suspect leads Traci and Andy to do the right thing. And when Luke and Jo work together on a surveillance job, they end up in each other's arms.
When a police informant is found murdered, 15 Division sets its sights on finding a weak link in the notoriously brutal East Jameson gang. Andy has to work closely with Detective Jo Rosati, a woman who seems far too interested in Andy's fiancé, Luke. Meanwhile, Gail finds herself protecting the life of the only known witness to the crime: a seemingly homeless 12 year-old boy with a shocking secret of his own.
When a woman gets brutally attacked in the same manner as deceased rookie cop Zoe Martinelli, Det. Luke Callaghan is convinced that it's the same suspect. But when his erratic behavior gets him booted from the case, he must convince Andy to put aside their differences and follow through on his theory- putting her in terrible danger along the way.
After a seemingly drunken man collapses in the barn, 15 Division is put under quarantine. Andy and Swarek work together to find the accomplice of a dyed blue bank robber. Gail Peck worries about her exposure to the sick man, while Chris goes undercover in a holding cell. And Dov's first date with a sexy bomb tech ends in a thrilling takedown.
Dov and Gail work together under Swarek's expert tutelage in a stake-out operation to stop an Asian gang from killing a snitch. Meanwhile, it Mounted Unit training day- Andy and Chris join the rookies from 27 Division in a competitive equine training event that gets Andy McNally back in the saddle, personally and professionally.
Andy, Dov, And Tracy are chosen to participate in an undercover exercise. They must all survive one night on the street after being dumped on the street with no money and no outside help in order to see how much money and drugs they can acquire by 6:00 am the next day. Dov runs in to one of his brother's old dealers and Andy and Tracy run in to Swarek while undercover and chance blowing his operation. Back at the station Chris and Gail deal with some teenage bullies.
Peck is accused of murder when responding to a shots fired complaint and one of the victims accuses an officer named Peck of killing his friend. Andy could have accidentally put Swarek in danger, when Brennan catches her in Swarek's apartment,Swarek turns up missing.