Tras el letal ataque a un convoy de la policía, AC-12 va por un despiadado sindicato del crimen organizado vinculado a oficiales corruptos.

Steve y Kate van tras una pista nueva y una filtración reciente provoca otra redada. Sale a la luz el vínculo de un oficial de alto rango con un grupo criminal.

AC-12 le pisa los talones a H, y Corbett idea un plan en el que McQueen requiere involucrarse con oficiales de la policía corruptos.

La identidad de la mente maestra es aún un misterio para AC-12, que solo tiene dudas. ¿Qué respuestas tendrán los contactos de Ted en Irlanda del Norte?

La búsqueda de H se intensifica, y Steve y Kate se preguntan qué es lo que Hastings oculta. Además, nueva evidencia genética desata una oleada de sospechas.

Mientras Hastings pasa por un interrogatorio implacable, se descubre una grabación secreta y la información conduce a una revelación impactante.

DCI Jo Davidson receives new information about the whereabouts of a suspect in the unsolved murder of investigative journalist Gail Vella. En route to raid the property, she spots an armed robbery in progress and stops the convoy. Suspicious of her motives, AC-12 launch an investigation. Still dealing with the fallout from their explosive investigation into undercover officer John Corbett, AC-12 soon realise they are facing their most enigmatic adversary yet.

Having opened an official inquiry into DCI Jo Davidson and Operation Lighthouse, AC-12 begin to suspect a cover up. Steve and Chloe dig into Gail Vella’s controversial reporting for clues to her murder, and find links to previous AC-12 cases. Their investigation takes a shocking turn when they begin to scrutinise Jo's personal life.

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, and tensions increase when Kate encounters a face from the past with links to organised crime.

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.

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.

As AC-12 struggle to deal with the repercussions of tragic events, Hastings makes one final bid to uncover institutionalised corruption before his time runs out.