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 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.
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.
While Nick Huntley faces lengthy questioning over his role in Tim Ifield's murder, AC-12 remain convinced of Roz's involvement.
After Sergeant Danny Waldron and his armed response team shoot dead a hardened criminal, cracks begin to appear in their story and AC-12 is assigned to investigate.
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.
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.
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.
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 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.
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.