After assaulting a Drug Squad officer, undercover detective John Moreland faces suspension. He gets a second chance when Detective Sergeant Rebecca Ellis recruits Moreland and his team into her newly formed Covert Investigations Unit (C.I.U.). The C.I.U.'s first case is to take down David Thorpe, an elusive drug kingpin Moreland has been hunting for years. Rebecca's leadership and her fragile relationship with Moreland are severely tested when Thorpe suspects that Moreland is a cop.

When a 15-year-old escort disappears at a sleek downtown hotel, the C.I.U. goes undercover to infiltrate an underage prostitution ring masterminded by two volatile brothers, Shaun and Paul Devlin. As Maria gets close to one of the brothers, she's haunted by memories of a savage beating suffered on a previous case. In a risky final play, Maria struggles to stay focused and safe as she takes on the escort ring's vicious leader.

A high-end litigator at a downtown law office goes missing, and his colleague Anna Quinn believes the firm's partners, specialists in corporate crime, are involved. Posing as an old friend of Anna's, Moreland cozies up to managing partner Christopher Locke - a guy with thousand dollar suits in his closet and a violent 'fixer' at the end of his phone. To expose the truth, Moreland engages Anna in a dangerous play.

An explosive gangland hit sends rookie officer Jesse Calvert back to his roots in order to find the supplier of the deadly assault rifles. Jesse reconnects with an old friend, gang member Isaac Tibbs, whose sister Heather was killed in the shooting. As Jesse works to re-establish his credibility with the gang's leader Monk, he learns the toughest lesson about being undercover.

Daniel infiltrates a group of deadly bank robbers. One of the gang members, Beth, starts flirting with Daniel provoking her possessive, erratic partner Colin to make a bold move. The team is forced to run a risky play to take down the heist crew.

Rebecca's ex-colleague Marcus Jakes is embedded with Ali Raman's gang of racketeers, whose interests include a vicious underground fight club. Rebecca still trusts him, but Moreland thinks Jakes has turned into a dirty cop. In an attempt to bust the extortionists and expose Jakes, Jesse gets into the ring and Moreland plays a guy looking to hire a contract killer.

Maria shows nerves of steel edging her way into an auto-theft ring that specializes in brutality and luxury cars. However, she's not nearly as brave in her private romantic life. On the play, she risks her safety and that of her colleagues by trusting one of the gang members with her true identity.

The C.I.U. believes a bad batch of drugs is killing young hipsters at an illegal after-hours club. Trying to ignore their attraction to each other, Khali and Jesse go clubbing, looking for answers. Jesse thinks he can score names from the cheeky bartender Beetle, while Khali's undercover skills are tested when she tries to tease information from the club owner. But the deaths are not overdoses, they’re murders. With the killer's gun aimed at Jesse, Khali makes an intensely emotional appeal to save his life.

No assignment is tougher than investigating fellow officers. Daniel's former Guns and Gangs unit, SMASH, is suspected of corruption. Under Daniel's guidance, Jesse poses as a recruit for the squad. After a brutal initiation, Jesse is accepted by SMASH leader Russell Hagler, Daniel's old mentor. As the C.I.U. closes in on the truth about SMASH, Jesse is in serious jeopardy, and in an attempt to save his colleague, Daniel makes a shocking confession.

Rebecca finally has the informant she’s been waiting for in Angie Sarich, the accountant for elusive and powerful drug kingpin Thomas Novak. Angie wants to work with the C.I.U. to take Novak down and start a new life for her and her son, but a shocking connection between Rebecca and Novak puts everyone at risk.

Diplomatic immunity prevents the homicide police from investigating a murder which occurs at an Eastern European consulate. The C.I.U. is called in on the case. Rebecca and Maria try to get through to the Consular Aide. Moreland and Khali take on the forceful, eccentric Consul. The team unravels an international network of human trafficking. But, will the Consul face justice? Will the women he has sold be found?

The C.I.U. must seize their one chance to infiltrate Devil’s Guard, a notorious biker gang that is behind the murders of innocent people. To do that, they are forced to trust the bikers' hitman Richard Dansky. Together, he and Moreland discover why the gang is targeting innocent people, and in a showdown with the volatile and erratic gang leader, they bring the bikers to their knees.

In the gripping season finale, all bets are off when Moreland's worst nightmare comes true. Eight years ago, he infiltrated Charlie Mulcair's gang. In the shoot-out that led to Mulcair’s arrest, his 12-year-old son was killed. Now out on parole, the convicted armed robber is bent on revenge. The vicious ex-con has been looking for Moreland and runs into him with his daughter Emily.