A botched operation leads Customs Officer 'Ash' to join a new undercover law enforcement team, that uses high-tech methods to catch high-level criminals. His knowledge of the street soon proves vital in tackling a major drug gang.
Tommy is finding the transition to his job with the Unit a difficult one. The team follows every move made by drug dealer Xavier, hoping he will lead them to someone bigger. But when he meets with a rival dealer things go very wrong.
The Unit use phone taps to help track a large sum of money in the hope that it will lead them to the 'Mr Big'. But they also lead the team to a family that Ash is determined to protect - despite their illegal activities.
Roach is feeling the pressure and so turns to a new supplier known as The Viking. However, the Unit are already monitoring the terrifying and ruthless Viking. An old friend of Ash puts her life in danger trying to assist him.
The unit discovers a link between the gang they have under surveillance and a batch of toxic pills. Phone taps lead Tommy to Paulo, a pizza delivery man being used to courier the dodgy pills for dealer, Scooter.
Roach turns to Yorkie, a violent armed robber, to try and solve his cash flow problems. The Unit are disturbed by the info they have on Yorkie but he could prove useful in penetrating the gang AND keeping the police off their backs.
Problems at home and at work are taking their toll on Ash, but he is convinced that the 'Mr Big' is up to something. A new player on the scene could lead to a breakthrough while Kim realizes her Ex-boyfriend has betrayed her.
With Roach feeling the pressure from inside and outside of his organization he becomes convinced that there is a traitor at work. As he attempts to find them he unleashes an unpleasant surprise for the Unit leading to a showdown.