Line of Duty returns for an explosive second series with another high octane police corruption tale. When a police convoy is ambushed by armed criminals, three officers are killed and a protected witness critically injured. Convinced that the gunmen were tipped off by a police source, AC12 - DS Steve Arnott (Martin Compston), DC Kate Fleming (Vicky McClure) and Superintendent Ted Hastings (Adrian Dunbar) joined by DC Georgia Trotman (Jessica Raine) - must track down the leak. Initially AC12's most valuable witness, suspicion soon falls on the sole surviving officer, DI Lindsay Denton (Keeley Hawes). In pursuit of their prey, AC12 find a web of corruption and vice with links to the very top of the force.