Harlee Santos takes drastic measures to cover up the murder of her abusive ex, Miguel. Lieutenant Matt Wozniak makes a deal with FBI Agent Robert Stahl to keep himself and his crew out of jail but soon discovers Stahl has led him into an impossible trap. As the crew deals with the fall-out from the failed heist, Tess struggles to keep her painful gunshot wound under wraps.

Following Wozniak's discovery that Stahl's target is his close friend and Mayoral Candidate, Julia Ayers, Wozniak launches an all-out war with Stahl. Meanwhile, Harlee dives into an investigation that takes an unexpected turn into her own past.

After Wozniak refuses to play ball with the FBI, Stahl turns up the heat on Harlee who lands in the middle of Wozniak's dangerous plan to free himself from the Feds by reeling in a bigger fish. Meanwhile, Internal Affairs Officer Verco applies pressure to each member of the crew to discover what really happened to Donnie Pomp.

Realizing that Stahl will stop at nothing to arrest Julia Ayre, Harlee decides to investigate on her own and determine whether there's any truth in his allegations of Ayers active business with the mob. Wozniak is confronted with a drug case that forces him to face the darkest demons from his past, his daughter's death, while exposing the origin of his loyalty.

Harlee and Wozniak investigate Caroline's murder, putting Harlee and Nava's relationship in an awkward place because she can't reveal her connection to the crime or the methods she will use to solve it. Wozniak focuses on determining which member of his crew is informing to Verco as Loman uncovers a much deeper secret.

Following Harlee's brave confession to the entire crew that she has been informing for the FBI, the team grapples with Harlee and Wozniak's betrayal. With their team falling apart, Harlee and Wozniak come up with a desperate plan to neutralize Bianchi. However, their actions have unforeseen consequences because the Mafia fires back.

Wozniak goes after Bianchi for breaking their agreement. Harlee seizes the opportunity to unite the team around an illegal mission to repay Tufo's brother's debt to a local drug dealer. Stahl heightens the stakes making good on his threat to go after the crew. Wozniak faces the impossible decision to pick between his team and Ayres just as his son, Nate, makes an effort to reunite.

Harlee makes the chilling discovery that someone is texting Cristina as her dead ex, "Miguel." The case of a missing kid leads Wozniak to uncover a local dealer who uses underage mules and reminds Loman of what their unit is all about. The crew gets caught in a brutal ambush.

Harlee and Wozniak lead a manhunt for the gunmen who ambushed the crew, and they unearth the key to taking down Bianchi. The crew bands together against Verco, who has evidence of their corruption. Stahl goes rogue to link Harlee to Miguel's death.

Harlee and Wozniak lead the crew on a dangerous mission to heist Bianchi's secret ledger and take down the mobster once and for all. But the plan takes a tragic turn when the events our heroes set in motion put one of their own in harms way, forcing Harlee to turn to an unlikely source for help.

Harlee helps Nava cover his tracks after a violent encounter, revealing a side of herself Nava's never seen before and putting their relationship in jeopardy. Wozniak faces a ghost from his past in order to take down a new enemy in his present. Stahl gets a critical piece of information in his hunt for the truth about Miguel.

In a dramatic confrontation, Wozniak faces the ally who betrayed him and makes his most difficult choice yet. Meanwhile, Stahl's fanatical plan to take Harlee down for murder finally pays off, forcing Harlee to get dangerously close to the man who's obsessed with her In the end, Harlee and Wozniak's desperate efforts to save themselves and the crew lead to shocking consequences for both.