Line of Duty returns for a second series, featuring a new police corruption story told over six one-hour episodes. The series opens explosively with the ambush of a police convoy in which three police officers are killed and a protected witness is seriously injured. The sole surviving police officer is Detective Inspector Lindsay Denton. Deputy Chief Constable Mike Dryden takes personal charge, assigning AC-12 to the case. Initially AC-12’s most valuable witness, the suspicion soon arises that Denton could be their prime suspect. In the pursuit of corruption, how far will they go to uncover the truth?