Series Twelve of Midsomer Murders premiered 19 March 2009, and concluded on 4 October 2009.
|Detective Chief Inspector Tom Barnaby||John Nettles||DCI Causton CID|
|Detective Sergeant Ben Jones||Jason Hughes||DS Causton CID|
|Woman Police Constable Gail Stephens||Kirsty Dillon||WPC Midsomer Constabulary|
|Mrs. Joyce Barnaby||Jane Wymark||Wife of DCI Barnaby|
|Ms. Cully Barnaby||Laura Howard||Daughter of DCI Barnaby|
|Dr. George Bullard||Barry Jackson||Chief pathologist of Midsomer County.|
|Overall Episode Number Within the Series||Series Number||Order Number||Title||Broadcast Date||Screenplay or Episode Writer||Director||Notes|
|67||12||1||The Dogleg Murders||19 March 2009||Andrew Payne||Richard Holthouse|
|68||12||2||The Black Book||26 March 2009||Nicholas Martin||Peter Smith|
|69||12||3||Secrets and Spies||7 July 2009||Michael Aitkens||Renny Rye|
|70||12||4||The Glitch||21 July 2009||Michael Russell||Richard Holthouse||Stephens transferred from uniform to CID becoming a DC.|
|71||12||5||Small Mercies||20 September 2009||Peter J. Hammond||Peter Smith|
|72||12||6||The Creeper||27 September 2009||Andrew Payne||Renny Rye|
|73||12||7||The Great and the Good||4 October 2009||David Hoskins||Richard Holthouse||This was the last episode of series twelve.|
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