Murphy is out posing as a criminal armourer to make an arrest. During the set-up he recognises Caz Miller, a man known for his connections to criminal gang leader and known cop-killer Dave Callard. Miller tells Murphy that he wants to kill another gang member called Richard Holloway. Murphy stops the planned arrest because he thinks he can gain Callard's trust and infiltrate the entire criminal organisation to take everyone out.

Callard recommends Murphy to the McGeechan brothers. They plan to reactivate some assault rifles, but won't tell Murphy why they need them. Murphy knows they plan something big, but first he has to make sure his cover isn't blown.

After months spent trying to nail gangster Dave Callard, suddenly Murphy has a bigger fish to fry: a wealthy hotelier called George Garvey with a taste for ethnic art. Murphy bumps into someone to whom Garvey's son owes a lot of money and manages to get closer to Garvey. To forget the pressure during work he starts to drink. It looks like only Ellie can save him now.

The operation against Callard builds to its conclusion as Murphy is hired to help complete a shipment of Afghan heroin into England. His undercover work could help secure the conviction, but Murphy's presence is demanded elsewhere, as a key prosecution witness in the High Court.

Callard starts systematically destroying the forensic evidence. Murphy and Miller fear that he may want to destroy one or both of them too.