Andy McNally’s first shift on the job turns into mayhem when shots are fired in a downtown rooming house. In the midst of the chaos, Andy triumphantly makes her first big arrest – a suspected drug dealer – who turns out to be Sam Swarek, an undercover officer from her own division. She makes up for her grave mistake by going face to face with a dangerous gunman who already has one man’s blood on his hands.

As the other rookies hunt down a dangerous escaped convict, Swarek drags Andy through his undercover haunts on a mission he won’t explain. At first, Andy assumes Swarek is a rogue cop trying to settle scores from his undercover days. Then she realizes two things: he’s actually trying to track down a missing informant whose life is in danger now that his cover has been blown; and, that there is an undeniable attraction between them.

While working on a high-stakes gun raid, Andy and Gail stumble upon a victim of domestic abuse whose brutal experience in the system has taught her not to trust the police. When Andy promises to protect the woman from her abuser, she soon learns that it takes more than just following protocol to be good at her job. Meanwhile, the other rookies get caught up in the annual police retirement boxing match – a fundraising event known as “Fite Nite.”

Andy’s undercover skills are tested – and found to be lacking – during a citywide campaign to clean up the streets, when she’s tapped to pose as a prostitute in order to arrest unsuspecting johns. But the real test comes when Andy and Dov inadvertently put a vulnerable street informant’s life in danger, and it’s up to the two rookies to infiltrate a dangerous gun deal in order to save the trapped woman from a group of ruthless criminals.

A home invasion at an upscale address leads to a massive first response call that brings out the training officers in full force. After the scene is cleared, Andy and Traci remain behind with the terrified homeowner. When Traci is called away to deal with an emergency with her son, Andy is left alone to face the armed thief who is still prowling around the house.

Andy’s romance with Det. Luke Callaghan gets complicated when he chooses her for a special assignment - serving a search warrant for a bullet lodged in the head of a witness to murder. When the witness escapes, Andy risks her life to apprehend him, but later finds herself at odds with Luke over the next steps in the case. Meanwhile, the other rookies discover the shocking truth behind evidence from a fatal traffic accident.

A severe heat wave wreaks havoc on the city, forcing the rookies to work around the clock to keep the peace. In the midst of the chaos, Andy discovers that a serial rapist may have resurfaced to prey on vulnerable teenage girls. And when the extreme temperature precipitates a citywide blackout, Andy finds she’s cut off from all backup and must take.

After their High School Outreach assignment goes awry, Andy and Chris stumble on the victim of a vicious beating behind a nightclub. When the trail of clues leads them to discover the man’s assailant was a cop, the rookies are faced with a gut-wrenching moral decision – a choice that could dramatically jeopardize their future on the force. Meanwhile, the senior officers compete in a retraining exercise led by Frank Best, the new acting Staff Sergeant.

After a routine speed trap leads to a messy accident on a city highway, Chris and Gail find one of the cars mysteriously empty and quickly realize that its license plate matches the one being broadcast in a citywide “Amber Alert” – a nine-year old girl has been abducted and the driver of the vehicle is the prime suspect. A whirlwind manhunt ensues involving a complex interrogation of the missing child’s parents. As always, everyone has a secret.

Andy’s attempt to avoid Swarek is thwarted when both are assigned to a prisoner transport. When things go awry and the inmate breaks loose, the two officers are led on a cat-and-mouse foot chase through the meandering woods. Meanwhile, Chris and Traci help Jerry reconstruct the missing notes of a vital court case, and Dov and Gail piece together the mystery behind an amnesiac John Doe.

What was to be a routine day for Andy is abruptly put on hold when her ex-copper father, Tommy, confesses that he might have committed a serious crime during one of his alcohol-induced blackouts while settling a score that has tortured him for years. As she and Swarek try to piece together what happened, little by little she begins to uncover the truth about the case that sent her father over the edge – evidence that could possibly send him to prison.

There’s a nervous tension in the air on Judgment Day for all the rookies at 15 Division who will have to undergo make-or-break assessments by Staff Sergeant Frank. But after the death of an unidentified girl at a house party – an emotionally harrowing experience that pushes all of her buttons – Andy begins to question whether she has what it takes to be a copper and contemplates handing in her badge.

Andy and Chris accidentally screw up one of the biggest drug busts of the decade when they arrest one of the players. In an effort to save the operation, Swarek and Andy go undercover to make the drug buy. When Andy realizes that their bait and switch has created an ambush that will endanger Swarek’s life, it’s all hands on deck as the coppers of 15 Division rush to save the life of one of their own.

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 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.

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. 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

Indications are that the East Jameson gang was involved in the murder 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. Stressed out with her mother at the station, Gail is tasked with protecting an eight-year-old boy who's the only witness to the crime.

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 murder, but his erratic behavior gets him kicked off the case. Andy may be in serious trouble when Luke urges her to follow through with his hunch on the crimes.

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.

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 Division 27 in a competitive equine training event that gets Andy back in the saddle - both personally and professionally.

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.

When Traci and Andy are sent out on an undercover training exercise, they stumble upon a young woman who is about to die of an overdose. Meanwhile, Dov finds himself on a “ride-along” with a drug dealer and old friend of his deceased brother. Back at the station, Chris and Gail deal with a teenage boy they found tied up at a graveyard; sifting through the wreckage of their relationship, to try to get to the bottom of a bullying situation.

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.

Blaming herself for Swarek’s mysterious disappearance and fearing for his life, Andy struggles to find a lead in the case. 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.