With time running out, AC-12 attempt to unmask 'H', the Fourth Man (or Woman) commanding the network of corrupt officers behind the murder of Gail Vella. But sinister and powerful forces appear intent on orchestrating a cover-up.

As AC-12 struggle to deal with the repercussions of tragic events, Hastings makes one final bid to uncover institutionalised corruption before his time runs out.

AC-12 link Gail Vella's murder with a historic case of police corruption, and Kate hatches a plan to tell once and for all if Jo is bent.They are closer than ever to cracking the case, but when Hastings' authority is undermined it leaves his team in a pot

DCI Jo Davidson faces increasing pressure from all sides as AC-12 make major breakthroughs in the investigation.Hastings acknowledges that the disciplinary action against him put Kate and Steve in a difficult position, and a forensic report from Farida's

On the strength of evidence from a new witness, DCI Jo Davidson brings Terry Boyle back in for questioning about Gail Vella's murder. Kate is torn between loyalty to Jo and wanting to assist AC-12's investigation, and tensions increase when Kate encounter

Having opened an official inquiry into DCI Jo Davidson and Operation Lighthouse, AC-12 begin to suspect a cover up. Steve and Chloe dig into Gail Vella's controversial reporting for clues to her murder, and find links to previous AC-12 cases. Their invest

When new information comes to light about a possible suspect in a year-long unsolved murder investigation, DCI Joanne Davidson appears keen to finally bring Gail Vella's killer to justice. However, after her conduct arouses suspicions, it's not long befor

In a nail-biting finale, closely guarded secrets are revealed.

As the hunt for 'H' intensifies, Steve and Kate wonder if Hastings is guarding a dark secret.

Tensions rise in the OCG following the events at Eastfield. With troubling questions hanging over the identity of ‘H', suspicions mount at AC-12.

Corbett's most daring plan yet requires McQueen to exploit links with corrupt police officers.

A fresh police leak enables another audacious raid, Arnott's attempts to gather information put him in a dangerous situation, and the team tries to contact the undercover officer.

Following the deadly hijack of a police convoy, AC-12 target a ruthless organised crime group known to have links with corrupt officers.

AC-12 pit their wits against Roz Huntley in a climactic duel to find Tim Ifield's murderer and unmask Balaclava Man.

AC-12's future hangs in the balance after Hilton bars them from investigating Roz Huntley. But Roz's problems are building closer to home.

Following shocking events, AC-12's investigation intensifies. The discovery of new forensic anomalies appears to provide them with a major breakthrough. Meanwhile, Nick Huntley comes under scrutiny.

As shocking new evidence is unearthed, AC-12 step up their investigation in to the case against Farmer. Could the real killer still be at large?

A dismembered body is discovered, and worries grow when Roz fails to report for duty. After further questioning of Michael Farmer unearths crucial new information, AC-12 challenge the case against him.

When DCI Roz Huntley captures a serial killer, Forensic Coordinator Tim Ifield alerts AC-12 to a possible miscarriage of justice.

DS Steve Arnott is arrested on suspicion of murder but continues to protest his innocence. DC Kate Fleming's undercover operation unveils unexpected facts, but will it hold the key to Steve's innocence and the identity of the Caddy?

Waldron's armed-response unit come under increasing scrutiny and again close ranks. But AC-12 feed new information to Kate that helps uncover cracks in their story. Arnott makes a shocking discovery, then his own past catches up with him.

When a criminal is shot dead by a police armed-response unit led by Sgt Danny Waldron, AC-12 gather evidence suggesting it was a deliberate killing rather than self-defence.

Arnott is convinced Gates played a part in Jackie's disappearance. With Fleming's help, the anti-corruption team tries to trap Gates into revealing his involvement in covering up Jackie's crimes.

Having been duped into covering up Jackie's crime, Gates is desperate to sever ties with her. But, as Arnott and Fleming close in on his secret, Gates is plunged into an even more dangerous situation than he first thought.