Line of Duty

AC-12 investigate DCI Jo Davidson's apparent mishandling of the murder of an investigative journalist.

AC-12 suspect a cover-up as they probe DCI Davidson's team to find the officer sabotaging the inquiry into Gail Vella's murder.

On the strength of evidence from a new witness, DCI Jo Davidson brings Terry Boyle back in for questioning about Gail Vella's murder. Kate is torn between loyalty to Jo and wanting to assist AC-12's investigation. Tensions increase when Kate encounters a face from the past with links to organized crime.

A new suspect in their sights, AC-12 rapidly move forward with their investigation. Hastings acknowledges that the disciplinary action against him put Kate and Steve in a difficult position, and Steve decides to delay his transfer from AC-12. An attempt to interview a key witness goes wrong, and the forensic report from Farida"s house upends the inquiry.

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

As AC-12 struggle to deal with the repercussions of tragic events, Hastings makes one final bid to uncover institutionalized corruption.

With time running out, AC-12 attempt to unmask 'H', the Fourth Man (or Woman) orchestrating the network of corrupt officers behind the murder of Gail Vella. But sinister and powerful forces appear intent on a cover-up.