When a Homicide investigation into the disappearance of a teenage babysitter fails to reveal any useful evidence, Church and Angie go undercover to infiltrate a sinister criminal family.

Someone is looking to hire a hitman, so Church goes undercover. Surprisingly, his client is a woman who claims that her husband is trying to kill her. She wants him dead before he succeeds.

A policeman has been shot. Undercover is called upon to infiltrate a suspected Romanian gang, but they don't deal with outsiders. Rocca must rely on an ex-undercover operative who could potentially jeopardize the job and the unit.

Undercover is called in to find a serial killer. When Angie's cover is blown, Kaye becomes her replacement. Her first solo job is going well until all contact with her is lost and she vanishes.

Following Kay's disappearance, the Unit goes into damage control, scrutinizing the surveillance footage and following up on the few leads they have - a process that provides an unexpected suspect.

Whilst undercover, Church is employed by a brutal mercenary, Cameron Fraser, to assist in the abduction of a young girl. After a botched attempt, Fraser successfully tails Church, putting the security of the unit at risk.

Following the drug-related death of a young clubber, the unit attempts to crack a large scale Ecstasy racket.

MacKenzie is put undercover on the witness protection scheme to befriend a victim of attempted murder because of her connections with a leading politician who is suspected of corruption.

While taking part in a buy/bust, Church and his dealer inadvertently get caught up in a siege instigated by three teenage criminals.

The Professional Integrity Unit investigates undercover over claims of corrupt handling. After evidence leads to Rocca's suspension, the unit wants to know what's going on.

Working undercover with bikies, Church sets up a buy/bust which turns sour after Stone is bashed and falls into a coma. Emotions run high as Church is forced to remain undercover.

After Stone is nearly shot during a meeting with a dealer, Mac is worried about Stone's well-being when an informant helps Stone penetrate a gun dealing ring.

The Unit goes undercover to locate a charismatic prison escapee, Kane, who accuses the police of wanting him dead rather than recaptured.

Stone and Angie go undercover to infiltrate "Mother Earth," a radical environmental group suspected of stealing explosives. Church is put in prison to befriend Aaron Feilder, the psychopathic leader of the group.

Church encounters Stone as part of the environmental extremist group. Stone wants to report to the unit but Church, driven by his own agenda, insists that any contact would jeopardise the sting.

Someone is killing prostitutes and when a second woman is found murdered, MacKenzie and Angie go undercover at a brothel.

When Church goes undercover to investigate a murder, he inadvertently ingratiates himself with the Rossis, a criminal family currently the target of an independent inquiry. Church is ordered to remain undercover.

With the help of the unit, Church manages to impress Dino Rossi and weaken the position of his right-hand man, who is resentful of Church being accepted into the ranks.

With Church recruited by the Rossis, Angie goes undercover to investigate one of Dino's contacts. Church is falling in love with Dino's sister, Christina, and may ultimately have to choose between her and the Unit.

While the Unit learns of Church's relationship with Christina, Church is forced to come to terms with Christina's involvement with the family business and refuses to testify against Dino.

Information comes to light that someone is trying to sell Dino details about Church. With his identity revealed, it is a deadly race against time for Church to save his relationship and his life.