John Mercer is serving a lengthy prison term for having killed his aunt and uncle. He is freed however by police and assigned to a special police squad that focuses on disorganizing organized crime. He is, in his own words, an assassin for the State and will be called upon to do anything that might be illegal. Hoping to undertake one job and then be let go, Mercer soon finds himself on the hook indefinitely. He's assigned to keep an eye on an undercover cop who may have leaked information about a major police operation resulting in the death of a senior officer.
Jude Cassidy, a police mole and member of a notorious criminal family is acquitted of killing a black youth and Lenny urges him to seek the protection of the fixers. Jude is reluctant to agree and John is not happy to mind him. When Jude is left alone under Calum's care the John's suspicions are confirmed.
The team's next target is Albanian mobster Tarek Sukoli, but, rather than rub him out, Lenny aims to make an example of him to other gangsters by destroying his drug dealing and prostitution rackets. Unfortunately this all goes wrong after one of the prostitutes freed by Calum is killed, as is a drug-dealer shot by Sukoli's hench-man after John advised him to refuse doing business with the Albanian. In the end it looks as if they will have to kill him after all.
Lenny wants John to assassinate Scott Glover, who has been found Not Guilty of murdering a young woman, but John questions his boss's motives and decides to keep Glover alive and gain his confidence in order to ascertain the true nature of the case.
John is tasked to kill a man, but the target is already one step ahead of him and ambushes him. John then discovers the man is his predecessor gone rogue, and possibly, what he himself may one day become.
John is instructed to kill Richard Blakeney, who is at the centre of a group of corrupt judges and high-ranking police officers who regard themselves as being above the law. To infiltrate their circle he gets to know Georgie, Blakeney's personal hit-man, but then he is invited to join the gang.