Line of Duty - Season 4

Line of Duty follows Detective Seargent Steve Arnott (Martin Compston), an former authorized firearms officer who led an operation to catch an Islamic terrorist intending to detonate a bomb, but the strike team mistakenly entered the wrong apartment and shot dead an unarmed innocent man. In the subsequent investigation Arnott refused to cover up negligence in the planning and execution of the raid and unable to work in his unit anymore, Arnott receives a transfer to AC-12, a unit tasked with uncovering police corruption. Arnott is partnered with D.C. Kate Fleming (Vicky McClure), a highly-commended undercover officer with a keen investigative instinct. They work under the supervision of Superintendent Ted Hastings (Adrian Dunbar), who is one of several Senior Investigating Officers responsible for uncovering corruption within the police force. Throughout the series, AC-12 investigate seemingly disparate cases involving seemingly-corrupt police officers, with each series focusing on a ...