New series. An attack is made on a police transport carrying seized drugs, leaving three officers dead. Suspicion immediately falls on the head of a criminal syndicate, who is suspected of having police officers on his payroll providing him with information. AC-12 are assigned to investigate and root out the corrupt cops - but realise they are up against their most destructive adversary yet. The return of Jed Mercurio's police thriller, starring Adrian Dunbar, Vicky McClure, Martin Compston and Stephen Graham.