Roz's husband Nick is brought in for questioning by AC-12. But while Nick denies any involvement in Steve's attack, his suspicions about Roz mount. (S4 Ep4)
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. (S4 Ep3)
Episode 1: DCI Roz Huntley is under intense pressure from her superiors to apprehend a serial murderer after months of fruitless investigation. (S4 Ep1)
AC-12's loyalties are divided when Steve Arnott comes under scrutiny from his colleagues. With his career in jeopardy, Arnott turns to an unlikely source for help. (S3 Ep5)
Fresh testimony launches AC-12 back on the trail of a corrupt officer with links to organised crime. But new disturbing evidence suggests the Caddy may reside within AC-12. (S3 Ep4)
DS Arnott believes there is a dark secret in Danny's past. DI Cottan is commended for cracking the Waldron case, while a spotlight falls on Arnott's conduct in a previous enquiry. (S3 Ep3)
Episode 1: Anti-corruption unit AC12 return for another investigation. Sergeant Waldron and his armed response team shoot dead a criminal, but cracks appear in their story. (S3 Ep1)
Rest in Peace: AC12's investigation exposes a vicious criminal gang run from within the police. Steve is convinced of Lindsay's innocence, but Kate is determined to prove she had a role. (S2 Ep6)
Bail Hearing: Lindsay is denied bail and is targeted in prison. Growing desperate, she tells Kate about a relationship with an executive officer and her theory of why she is being framed. (S2 Ep3)
In the Line of Duty: Following the tragedy at the hospital, AC12's Kate is planted undercover in Lindsays Missing Persons Unit. But Lindsay in turn gathers compromising evidence. (S2 Ep2)
Status Zero: An ambush on a police convoy leaves three officers dead and a witness fighting for his life. AC-12 turn their spotlight on the officer who led the convoy but escaped unscathed. (S2 Ep1)
Terror: Pressure mounts on Gates as he is hounded by blackmailers. Desperate for proof of Gates's corruption, Fleming pushes their relationship to the limit. (S1 Ep4)
In the Trap: After being attacked, Gates tampers with evidence as the police rush to the scene. But Arnott remains suspicious, convinced Gates played a part in Jackie's disappearance. (S1 Ep3)
After a bungled raid, Steve Arnott is transferred to an anti-corruption squad, where superintendent Ted Hastings gives him a 'very special' case to investigate. (S1 Ep1)