DS Steve Arnott is arrested on suspicion of murder but continues to protest his innocence.

Loyalties are divided when DS Steve Arnott comes under scrutiny from his colleagues.

While Nick Huntley faces lengthy questioning, AC-12 remain convinced of Roz's involvement.

Tensions rise in the OCG following the events at Eastfield. With troubling questions hanging over the identity of ‘H', suspicions mount at AC-12.

DCI Jo Davidson faces increasing pressure from all sides as AC-12 make major breakthroughs in the investigation, but an attempt to interview a key witness goes horribly wrong.

As the hunt for 'H' intensifies, Steve and Kate wonder if Hastings is guarding a dark secret.

AC-12 link Gail Vella’s murder with a historic case of police corruption, and Kate hatches a plan to tell once and for all if Jo is bent. They are closer than ever to cracking the case, but when Hastings’ authority is undermined it leaves his team in a potentially dangerous situation.

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

In a nail-biting 90-minute finale, Hastings's secrets are laid bare. Will 'H' be revealed at last?

Lindsay fights for her life as troubling details emerge of a vicious conspiracy involving corrupt police officers. With growing evidence of links between DCC Dryden and the ambush, Hastings is under pressure to arrest his senior officer.

Following the deadly hijack of a police convoy, AC-12 target a ruthless organised crime group known to have links with corrupt officers.

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

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 brutal ambush on a police convoy leaves three officers dead and a protected witness fighting for his life. AC-12 turn their spotlight on Lindsay Denton, the officer who led the convoy but escaped unscathed.

Following the tragedy at the hospital, AC12's Kate Fleming is planted undercover in Lindsay Denton's Missing Persons Unit. But Lindsay in turn gathers compromising evidence against the anti-corruption team.

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.

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

Following the violent attack she suffered in prison, Lindsay is granted special dispensation to visit her dying mother. Meanwhile, deputy chief constable Dryden shrugs off allegations about his relationship with Lindsay and possible links to the ambush.

DS Steve Arnott believes there is a dark secret in Danny Waldron's past.

Fresh testimony launches AC-12 back on the trail of a corrupt officer.

DCI Roz Huntley is under intense pressure from her superiors to apprehend a serial murderer after months of fruitless investigation.

With Gates on the run, the anti-corruption team come under pressure to close the case once and for all. Arnott is forced to make some tough decisions about where his loyalties lie. Fleming and Hastings go all out to catch Gates, leading to a shattering conclusion.

After the shooting at the drugs house, DC Fleming increases the pressure on Danny Waldron.

Lindsay is denied bail and finds herself targeted in prison. Growing increasingly desperate, she tells Kate about a relationship with an executive police officer and her theory of why she is being framed.

AC12's investigation finally exposes a vicious criminal gang run from within the police. But while Steve now appears convinced of Lindsay's innocence, Kate remains determined to prove she had a role in the ambush.