Mould

Middle-aged divorcee Susie Bishop is found dead, and the team quickly learn she lived a far racier private life than her neighbours would have guessed. The neighbours' version of Susie does not survive contact with the investigation. Two men were fighting over her, she was still seeing her ex-husband, and she was having a fling with the married headmaster at the school where she worked. One of the men has an alibi. When the alibi falls apart, the killer's identity is a genuine surprise.

Then a second body turns up: a woman with a green face, dressed in a sexy policewoman's outfit, dead in a field at Dob Cross. Gill is convinced the killer here is a lover, which tells you how the rest of the hour will go.

The personal lives are in their usual state. Gill has to reject her ex-husband Dave's drunken pleas for a reconciliation, then leave a briefing on a mercy dash because Dave is too drunk to look after himself, and she needs Janet's help to get him round to his mother's. Rachel is shaken to discover that Sean has been married before and has a little boy, who takes against her on sight. Sean keeps acting as if they are getting married; Rachel keeps insisting they are not. When she takes a can of beer out of Dom's hand and warns Sean that her brother has a drink problem, you can see the whole fragile arrangement wobble.

Diane Taylor and Sally Wainwright wrote it, Paul Walker directed. Suranne Jones's Rachel, Lesley Sharp's Janet and Amelia Bullmore's Gill lead, with Julia Deakin as Scary Mary Jackson, Sean Maguire as Sean, Nicholas Gleaves as Andy, and the squad in support.

A murderer who turns out to be someone you would never pick. And a set of personal lives all stuck in the same low gear. The mix is the show's whole trick, and it still works.