November 2011 in the Wessex coastal borough of Old Winton and Winton on Sea. An investigation into an alleged sexual assault by PC Steven Porter on his colleague PC Janet Tate by police Professional Standards officers has been abandoned as vital evidence is lost. On late shift both officers are called to a road traffic accident. Later in a deserted car park they quarrel. Tate draws her baton and savagely beats Porter who after signing himself out of A&E, dies in his sleep. Councillor Cedric Hailey, Old Winton's council member for law and order and one time wannabe cop is scoring political points by calling for no stone to be unturned to find Porter's killer. Quickly discovering the truth detectives DS Constancia Dunne and DC Jason Kelly work to build a case of mitigating circumstances and to discover if the Professional Standards investigation was derailed by Undue Influence.