DS Tommy Murphy is called back to work after a leave of absence to be at his mother's side. His new job is to attempt to get close to Drew and Billy Johnstone, vicious Belfast criminals now operating in Leicester. Murphy thinks he's found himself a way in when a drug deal goes awry.

Working deep under cover, Murphy manages to gain the trust of Billy Johnstone, while trying to uncover the associations between his brother Drew and a local Asian criminal network.

Murphy ends up being exposed and caught up in a vicious and final showdown between brothers Drew and Billy Johnstone.

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.

Murphy tries to get counterfeit Euros for Callard, and asks fellow undercover officer Jill Calder for help. She has infiltrated an organisation that is printing the fake money. Together they try to set up a deal for both their clients and plan to make the big arrest during the handover.

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.

The hunt for a serial killer who is stalking London’s West End becomes personal for Murphy when tragedy strikes at the heart of the investigation.

Parmer, a promising young police officer, has apparently committed suicide. Murphy is sent undercover to find out whether he was a victim of racist bullying.

Murphy has been asked by Interpol to be a part of an operation to infiltrate an international car-ringing gang. Soon he finds himself paired up with philosophising French agent, Benoit.

Murphy must go undercover in a biotech laboratory and comes up against a powerful adversary whom he cannot see.

A novice nun has apparently committed suicide and soon another nun mysteriously disappears. Murphy goes under cover as a priest to investigate.

Three convicted murderers have now been murdered themselves. The three have one thing in common: they have been named in a campaign run by a support group for relatives of murder victims. Murphy must find out if this is a coincidence or if someone if murdering convicted killers just for revenge.

Murphy infiltrates a gang implicated in a series of diamond heists and finds himself out of his depth involving Japan's equivalent of the mafia. Complicating the situation, Murphy finds himself attracted to Annie.

Richard Mooney, London's most infamous kidnapper, is brought in, and the race is on for Annie and Murphy to get a confession in time to save the life of his latest victim, Kate Jennings. To crack Mooney’s silence, Murphy is set up as a suspected terrorist and goes under cover into Bellview Prison to befriend him. But when this master plan is unexpectedly threatened by the prison's very own protection racket, time seems to be running out for Kate.

When Mickey Munday, a world-famous Irish snooker player, comes under pressure to rig the outcome of his game in the forthcoming championships, Murphy and Annie go undercover to protect his life and find the culprit when he arrives in London. The stakes are raised for Munday when his long-lost love and daughter reappear in his life.

In the glittering world of London’s West End club scene the head of security of a well-known East End gang is found murdered. The prime suspect is another gang leader, Carl Tate. In order to prevent another "door wars", Murphy joins Carl's gang undercover, but when warfare escalates Annie is compelled to join ranks with Murphy on the doors of Carl's latest venture, X-Club.

Following a bungled attempt to close down an elaborate Russian crime-ring, Murphy and Annie find themselves embroiled in what appears to be a textbook crime of passion. An unknown blonde is busy murdering London's successful business people. The only common link is that all the victims are members of a state-of-the-art health club in the heart of the City.