Blaming herself for Swarek's mysterious disappearance and fearing for his life, Andy struggles to find a lead in the case. She's right to worry-- Swarek is being brutalized by a vicious gangster with a vendetta. Will Andy and the other rookies find him in time? Little do they know that shocking events triggered by this investigation will incriminate one of their own and may also put an end to Andy's career.

When Gail's uniform is stolen from her car, she and the other rookies from Division 15 attempt to catch a cop-impersonating vigilante. A drug deal gone awry may offer clues to help Chris and Dov unravel the motive behind the cop masquerade. Meanwhile, Andy and Sam's inability to stay away from each other poses a life-threatening risk to Swarek.

Andy, Dov and Traci are tested with a challenging undercover training exercise, but things go awry when Andy and Traci run into Swarek on his own undercover operation, and they must tread carefully not to blow his cover. The women stumble on a young woman who is overdosing and risk blowing their own cover to save her life. Meanwhile, Dov finds himself on a "ride-along" with a drug dealer who was an old friend of his dead brother's, and faces a choice that could threaten his career. Back at the station, Chris and Gail deal with a teenage boy they found tied up at a graveyard, but must sift through the wreckage of their relationship to get to the bottom of a bullying situation.

In the course of pursuing a kidnapper, Andy and Swarek come upon a terrible accident with a woman pinned in her car. While Swarek tracks the missing child and his kidnapper, Andy stays behind with the critically injured woman. The rest of the 15th Division gets in the chase to catch the kidnapper, but Chris comes to blows with Dov over an indiscretion involving Gail. Meanwhile, Andy is galvanized to take bold action when she realizes life may be passing her by while she is making other plans.

It's a race against the clock as Dov and Gail work under Swarek's expert tutelage in a stakeout operation to stop an Asian gang from killing a snitch. Meanwhile, at Mounted Unit training day, Andy and Chris join the rookies from 27 Division in a competitive equine training event that gets Andy back in the saddle—both personally and professionally.

Division 15 is thrown into a panic when a seemingly drunk man that Gail and Traci brings in collapses from a mysterious illness and everyone is placed under a quarantine. Meanwhile, Andy and Swarek team to apprehend and book an unusual suspect in a brutal bank robbery - a man covered with blue dye. But will they uncover the identity of his violent partner? And as time ticks down, the squad grows increasingly nervous about the quarantine, with Gail worrying about her exposure to the sick man. Also, Dov's first date with a sexy bomb technician ends in a thrilling takedown.

Andy is worried that her personal problems are clouding her professional judgment when a woman is brutally attacked on her watch. Detective Luke Callaghan is convinced that it's the same suspect when the details of assault are alarmingly similar to the unsolved murder of a rookie. Ironically, Andy is caught in between dueling theories of the crimes—one supported by Luke, the other by Jo Rosati. But when Luke is booted from the investigation because of erratic behavior, he tries to get Andy to follow through on his hunch—putting her in serious danger.

When a police informant's murder points to the involvement of the notoriously brutal East Jameson gang, the division realizes that cracking this case will not be easy. And when Gail's intimidating mother, Superintendent Elaine Peck, arrives on the scene, there is even more pressure to solve the case. Meanwhile, Andy finds herself paired with Detective Rosati, whose unintentional disclosure of a secret puts Andy's relationship with Luke in jeopardy. And Gail, stressed out by her mother's presence in the station, is assigned to protect the only known witness to the crime -- a seemingly homeless eight-year-old boy with a shocking secret of his own.

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. Trapped together in a hotel room, the two detectives finally have it out over their past, raising the question of whether they are really finished.

As the 15th Division attempts to recover from an explosive event involving one of their own, a series of arsons culminates in the torching of a laundromat. The list of suspects grows, as 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, Andy's effort to stop the grieving widow from entering the burnt-out laundromat resultS in the two women being trapped in the unstable building, and what seems like a straightforward case of arson ends up being something much bigger.

As a full moon hangs over the city, the rookies are unnerved by a series of strange occurrences. While investigating the bizarre theft of three severed heads from a medical lab, Andy and Swarek track a disturbed man whose obsessive behavior makes him suspect. In an effort to protect the life of a young woman who may be the next target, Andy places herself - and, inadvertently, Luke - in a potentially fatal situation.

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 involved with a vicious criminal. Meanwhile, Traci wrestles with feelings for her old flame, Detective Barber, Dov tries to weather the storm when a young woman files a complaint against him, and Andy unwittingly opens up to Sam about her commitment to Luke.

Five young and ambitious rookie cops continue to navigate the emotional trials and tribulations of their professional and personal lives. Last summer these rookies hit the streets for the first time with their training officers and learned how to walk the thin blue line. Now the training wheels are off. More experienced, they're ready to kick some serious butt. But these rookies are just beginning to realize there are no shortcuts to being successful at this job. And when you're a rookie officer, a little knowledge is a dangerous thing, as they discover.