<P> Line of Duty is a BBC police procedural television series created by Jed Mercurio starring Martin Compston and Vicky McClure as Steve Arnott and Kate Fleming; detectives assigned to an elite anti-corruption unit designated AC - 12 . The stories follow investigations into suspected corrupt police officers, at the behest of Superintendent Ted Hastings (Adrian Dunbar). They are Lennie James as DCI Tony Gates, Keeley Hawes as DI Lindsay Denton, Daniel Mays as Sergeant Danny Waldron and Thandie Newton as DCI Roseanne Huntley . Numerous characters appear outside of their initial arcs, including Hawes' reprisal of her second series role during series 3, and Craig Parkinson's reprisal of his role during both series 2 and 3 . To date, 23 episodes have aired, with the first and fourth series linked thematically, and the second and third series similarly connected: however, all series have a single overarching connection, with all series referring to the same criminal network involved in the events of each series' plot . </P> <Table> <Tr> <Th_colspan="2"> Series </Th> <Th> Episodes </Th> <Th_colspan="2"> Originally aired </Th> <Th> Ave . UK viewers (millions) </Th> </Tr> <Tr> <Th> Series premiere </Th> <Th> Series finale </Th> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> 5 </Td> <Td> 26 June 2012 </Td> <Td> 24 July 2012 </Td> <Td> 3.80 </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> 6 </Td> <Td> 12 February 2014 </Td> <Td> 19 March 2014 </Td> <Td> 3.43 </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> 6 </Td> <Td> 24 March 2016 </Td> <Td> 28 April 2016 </Td> <Td> 5.42 </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> 6 </Td> <Td> 26 March 2017 </Td> <Td> 30 April 2017 </Td> <Td> 9.55 </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Series </Th> <Th> Episodes </Th> <Th_colspan="2"> Originally aired </Th> <Th> Ave . UK viewers (millions) </Th> </Tr>

How many episodes in season 1 line of duty