Darren Treacy återvänder till Dublin, för att fira sin bror som blir frisläppt från fängelset, efter att ha lämnat i all hast ett år tidigare.

Darren spårar Jimmy Byrne, ledaren för en misstänkt gängmord.

Spänningarna och misstänksamheten ökar inom gänget när Darren närmar sig sanningen. Darren är osäker på sina känslor för Rosie.

Dagen för Nidge och Trishs bröllop anländer. John Boy och Hughie startar en rekrytering inför det kommande kriget och Darren kämpar med att skydda Mary och barnen från konflikterna.

In debt to loan shark Fran, gang footsoldier Darren finds he has no choice other than to turn back to his former mentor, northside kingpin John Boy Power. Under pressure from the cops and doing way too much cocaine, John Boy is becoming paranoid and erratic. John Boy agrees to take on Darren’s debt in return for absolute loyalty – the deal with the Devil done, Darren is back on the team...

Disaster strikes the gang as a drug mixing factory is busted by the gardai. John Boy blames Stumpy who he believes sold them out. Darren, desperate to get out of the game, robs an ATM machine and makes a downpayment to John Boy against the debt he owes. John Boy, however, wants Stumpy taken care of and he wants Darren to be the one to deal with it.

When a container of drugs is busted at the docks, John Boy decides to double cross Fran on their deal. Fran retaliates against John Boy. John Boy is furious and orders Nidge to pipe bomb Fran's house leaving Fran determined that the escalating gang war will not end until he has revenge.

The crew are in festive spirits as Trish has the baby on Christmas Eve, while Rosie has come back to Dublin and Darren falls in love with her all over again. However the gang war is still raging, and John Boy orders Tommy – already caught between his friendship with Debbie and his worries about Siobhan’s money runs – to kill Fran. The hit goes wrong, and someone else becomes fatally caught up in the aftermath.

As tensions come to a head the gang threatens to implode: Luke's obsession with Mary is becoming more dangerous, while Siobhan's panic attack at the airport could get Tommy killed. Paranoid John Boy finally tips over the edge of sanity when he finds Debbie taking heroin.

Nidge swiftly fills the power vacuum and gets the gang back to business as usual. Rosie has realised what her lover has become, and Darren is devastated when she breaks up with him. Meanwhile Mary finally realises the extent of Luke's psychosis as she finds him lurking in her bedroom at night.

When one of his gang is mistakenly shot by a rival organisation, Nidge plays the diplomat... but a mad drunken Paddy's night slides out of control towards disaster.

Nidge sets out to persuade Dano that he had nothing to do with his father's disappearance but a scapegoat must be found. Nidge turns to ever faithful Darren for help.

Nidge struggles to allay Dano's suspicions when his secret threatens to get out as Siobhan and Elmo, for different reasons, start to talk.

Pressure builds on Nidge as the leaders of Dano's organisation send an inquisitor down from the north to thwart him, and matters only get worse as his lies start to catch up with him.

As both Dano and the Gardaí begin to put the puzzle together, what can Nidge do to stay ahead and stay alive?

The truth about Paddy's night is out. Boxed into a corner Nidge contemplates a new life in Spain - but soon realises it's only a matter of time before Dano catches up with him.

Dublin gang boss Nidge has been blooded and has proved his mettle. He has killed friend and foe to become King. But the throne is a dark and lonely place.

Nidge coerces his dentist into cooperating with him, unaware that Detective Inspector Moynihan is setting up a complex undercover operation to track and ultimately bring him down.

Fran, still afraid that he could go down for the tiger kidnapping, lashes out looking for someone to blame. Resulting in a serious challenge to Nidge's authority.

Moynihan's surveillance operation closes in on Nidge and Andrew's dummy run bringing in a shipment of mixing agent, while Fran plots a gruesome revenge.

Nidge's preparations for the import operation are disturbed by an unwelcome encounter with a ghost from his past, and Nidge will do anything to prevent a terrible truth getting out. Isolated and increasingly paranoid, Nidge finds solace in his relationship with Janet and fails to notice that Moynihan and his undercover team are closing in on one of the conspirators...

As the shipment of drugs arrives at Dublin port, the deadly game of cat and mouse between Nidge and Moynihan reaches its climax.

After almost losing everything to D.I. Moynihan’s sting operation, Nidge travels to Spain to negotiate with a wholesale supplier for a new drugs shipment. Meanwhile, Patrick has returned to Dublin to exact revenge, and tensions between Fran and Nidge reach boiling point.

With Pauley’s help, Nidge is back in business and arrangements are made for the first shipment under the new deal. Meanwhile Moynihan wrestles with a labyrinthine Garda bureaucracy.

Fran is banged up in prison but he and Nidge both still conspire to have each other killed, while Siobhan finds her dangerous drug fuelled double life is spiralling out of control.

Nidge uses Scotty as a driver on a new job, while Siobhan learns Tommy will soon wake from his coma and finds herself caught between her quest for revenge and her love for Pauley.

In the aftermath of Pauley’s death Siobhan must face her most terrifying opponent yet as Terence May flies in from Spain to lay his nephew to rest—and to find the truth.

Nidge is summoned back to Spain, where Terence demands a terrible price for his continued support, while Siobhan and Moynihan reach an unholy deal of their own.