The AC-12 anti-corruption unit, led by Ted Hastings, Kate Fleming and Steve Arnott, faces a new case as suspicions surrounding H's mysterious identity begin to point to someone they never expected: Hastings.

As the hunt for `H' intensifies, Steve and Kate can't help but wonder if Hastings is keeping a dark secret.

Tensions rise in the OCG following the events at Eastfield, and 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; AC-12 makes a shocking discovery.

Kate and Steve attempt to track down a lead; a fresh police leak enables another audacious raid; Steve's attempts to gather information put him in a dangerous situation.

When three police officers are shot to death during the hijack of a seized-drugs transport, AC-12 move in to investigate possible police collusion; As the body count rises, the team realize they are up against their most destructive adversary yet.

While Nick Huntley faces lengthy questioning over his role in Tim Ifield's murder, AC-12 remain convinced of Roz's involvement.

DCI Roz Huntley struggles to allay her husband's suspicions. AC-12 find a new angle to pursue their case against her.

Nick is brought in for questioning by AC-12, but while Nick denies any involvement in Steve's attack, his suspicions about Roz mount. AC-12 discover new anomalies in the forensic evidence and issue DCI Roz Huntley with a second Reg 15 notice.

As AC-12 wrestle with the new forensic evidence casting doubt over Tim Ifield, Kate is approached by another woman claiming to have been assaulted by Michael Farmer.

A dismembered body is discovered, and worries grow when DCI Roz Huntley fails to report for duty. AC-12 crank up their investigation into Operation Trapdoor, concerned that Michael Farmer will go to jail for crimes he didn't commit.

DCI Roz Huntley is under intense pressure from her superiors to apprehend a serial murderer after months of fruitless investigation. When another young woman is abducted, Roz is on the scene to track down and charge a 24-year-old man.

DS Steve Arnott is arrested on suspicion of murder.

AC12's loyalties are divided after DS Steve Arnott comes under scrutiny from his colleagues.

Fresh testimony launches AC-12 back on the trail a corrupt officer with links to organized crime.

DS Steve Arnott believes there is a dark secret in Danny Waldron's past. But while DI Cottan is commended for cracking the Waldron case, the spotlight falls on Arnott's questionable conduct in a previous enquiry.

After the shooting at the drugs house, DC Kate Fleming uses her undercover role to increase the pressure on Danny Waldron's armed response unit. Meanwhile, a previous AC12 investigation comes under legal scrutiny.

Sergeant Danny Waldron and his armed response team shoot dead a hardened criminal.

AC12's investigation finally exposes a vicious criminal gang run from within the police.

Lindsay fights for her life as troubling details emerge of a vicious conspiracy.

Lindsay is granted special dispensation to visit her dying mother.

An obsessed man unable to accept the abduction of his young son spends years searching for him.

Detective Sergeant Nancy Devlin struggles to hide her longstanding connection to a drugs trafficker.

A Missing Persons Field Unit is tasked with tracking down serial killers.