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.
As the hunt for "H" intensifies, Steve and Kate wonder if Hastings is guarding a dark secret.
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?
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.
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.
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.
DS Steve Arnott believes Danny Waldron compiled a list of his childhood abusers; while DI Cottan is commended for cracking the Waldron case, the spotlight falls on Arnott's questionable conduct in a previous enquiry.
Lindsay Denton sets out to clear her name, while Arnott and Hastings interrogate Bains on suspicion of murder.
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.
DS Steve Arnott is arrested on suspicion of murder.
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.
Lindsay finds herself targeted in prison and tells Kate her theory of why she is being framed.
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.
Having been duped into covering up Jackie's crime, Gates is desperate to sever ties with her; as Arnott and Fleming close in on his secret, Gates is plunged into a more dangerous situation.
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.