Deep undercover, Sergeant Smith meets arms dealer Darren Cutler, his nephew Kieran Wallace and Tommy Rose, a member of the notorious SE1 gang. Tommy hands the sergeant a gun and insists it has never been used, but Smithy realises otherwise.
After a briefing with DC Stevie Moss and DS Max Carter, they discover the gun has been used in a recent murder and they need the weapon to find the suspect. Posing as Smithy’s girlfriend, Stevie is able to sneak the gun away from Wallace, but Smithy is adamant he needs it back as quickly as possible, or face serious consequences.
Max takes a huge risk by deciding to plant the gun in Wallace’s car, in order to pull him over and ‘discover’ the weapon. Stevie nearly gets caught by Wallace hiding the gun in his car but Smithy smashes the vehicles’ rear light so the patrol car can pull them over.
Wallace is finally arrested while Smithy meets up with a furious Cutler who demands to know why the gun was in his nephew’s car. When Smithy asks if Wallace will keep his mouth shut in prison, Cutler responds by pulling a gun on Smithy.