When three police officers are shot dead during the hijacking of a seized-drugs transport, AC-12 moves in to investigate possible police collusion.
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.
Corbett's most daring plan yet requires McQueen to exploit links with corrupt police officers; AC-12 makes a shocking discovery.
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.
As Hastings's secrets are laid bare, Kate and Steve are torn between loyalty and their duty to uncover the truth. Will the identity of "H" be revealed at last?
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.
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.
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.
DCI Roz Huntley struggles to allay her husband's suspicions. AC-12 find a new angle to pursue their case against her.
While Nick Huntley faces lengthy questioning over his role in Tim Ifield's murder, AC-12 remain convinced of Roz's involvement.
Sergeant Danny Waldron and his armed response team shoot dead a hardened criminal, but soon cracks appear in their story.
DC Kate Fleming uses her undercover role to increase the pressure on Danny Waldron's armed response unit; an old AC-12 investigation comes under legal scrutiny.
Fresh testimony puts AC-12 back on the trail of 'the Caddy,' a corrupt cop with links to organized crime.
AC-12's loyalties are divided when DS Steve Arnott is suspended from duty; with his career in jeopardy, Arnott turns to an unlikely source for help.
Arnott is arrested on suspicion of murder, and DC Fleming's undercover operation may hold the key to his innocence and the identity of the mysterious perp.
A brutal ambush on a police convoy leaves three officers dead and a protected witness fighting for his life; AC-12 turns their spotlight on the officer who led the convoy.
Kate Fleming is planted undercover in Lindsay Denton's Missing Persons Unit.
Lindsay is granted special dispensation to visit her dying mother.
Lindsay fights for her life as troubling details emerge.
AC12's investigation finally exposes a vicious criminal gang run from within the police.
Steve Arnott discovers his target is the city's top detective, Tony Gates.
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.
Desperate for proof of Gates's corruption, Fleming pushes her relationship with him to the limit; her behavior causes Morton to question if she might not be such a loyal colleague after all.
With Gates on the run, the anti-corruption team comes under pressure to close the case; Arnott is forced to make some tough decisions about his loyalties; Fleming and Hastings go all out to catch Gates.