Mackenzie is faced with a choice between her personal happiness and her successful career when she becomes involved with a charismatic art thief who entices her into believing that love is more important than the law.

The Unit seems on shaky ground when Homicide attempt to charge Church with the murder of Denny Kaplan, but are devastated when Stone goes beyond the call of duty to save Church.

When the Unit try to nab a standover man for murder, Angie's relationship with informant Marty Engle results in a confrontation within the ranks and the Stingers having to face the fury of one of their own.

Church becomes convinced he is being stalked by a man who holds him responsible for the murder of his girlfriend, causing him to jeapordise the Unit's current operation, busting an illegal tobacco ring.

Stone heads undercover to expose a high powered businessman, but experiences a crisis of conscious when he discovers a young prostitute he has cared for is in danger as a result of his actions.

Working with criminal profiler Vicki Quinlan and the new Head of Homicide Frank Callahan, the Undercover Unit investigate a serial murderer but their attempts to trap the killer leaves Mackenzie fighting for her and her best friend's life.

When an undercover operation causes the death of a young woman, Church and Angie are faced with the dilemma of saving one dangerous criminal from another.

When a failed drug bust leaves the Undercover Unit with a dead dealer high class prostitute holding a couple of bags of cocaine, the Unit undertake an operation inside a busy brothel: Gotham City.

Stone is abducted when Undercover's attempt to bust an international arms dealing ring, run by lethal ex SAS officers, fails.

Stone and Church go undercover to investigate a pair of teenage drug manufacturers, with unexpected tragic consequences.

Undercover teams up with Armed Robbery to bust a violent robbery ring. Church infiltrates the group but is forced to bow out when he is given a shotgun and told to rob a convenience store.

With Harry Love in a position to make his final move against Mackenzie, she and the Undercover Unit are forced to take desperate action, with tragic consequences.

Angie and the rest of the Undercover Unit rally around Mackenzie, risking their jobs in order to prove her innocence.

Stone goes undercover as a hitman to investigate a woman who is organising a hit on her husband, while Mackenzie is dealing with hitmen of a different kind when she finds herself the suspect in a murder.

Danni has to protect former undercover cop Gary Edgerton, a reluctant key witness in the trial of a major criminal, and help him prepare for his court appearance.

Angie is forced to bend the rules as she attempts to prevent her sister Sam from being arrested on drug importation charges.

When Church is sent undercover to share a cell with a convicted murderer, Danni must face the toughest decision of her life alone.

Stone cultivates a live-wire young prostitute named Brittany to get information on a dangerous drug crime. Church and Danni move into their new home

Mackenzie discovers the grifter who drugged her is linked to a senior colleague - someone who has good reason to want her out of the running for head of Homocide.

Danni's determination to go it alone with her pregnancy clouds her professional judgement when she stumbles across an illegal adoption racket.

Angie faces one of her toughest cases yet when she has to develop a romantic relationship with a murder suspect and then coerce him into becoming an informant.

Mackenzie becomes the victim of a grifter on the eve of her interview for Head of Homicide. Meanwhile, Church finds his career threatened when a journalist attempts to expose him in a newspaper article.