What begins as a seemingly routine night ends in tragedy for WPC Kathy Marshall (Lynne Miller). DS Don Beech (Billy Murray) continues to play both sides of the law against the middle, DS John Boulton (Russell Boutler) strives to prove himself, and PC Mike Jarvis (Stephen Beckett) takes part in the Advanced Driving Test at Hendon. In the race to become the next Sun Hill Sergeant, will June Ackland (Trudie Goodwin) or Gary McCann (Clive Wedderburn) have a good night out? WDC Liz Rawton (Libby Davison) joins the Sun Hill CID team and immediately finds herself accused of framing a drug addict, and an old friend of DCI Jack Meadows (Simon Rouse) stands accused of murder. Marking the 1000th episode, disaster strikes Sun Hill when a tanker crashes, spilling a potentially lethal near a housing estate.

The twelfth series features notable guest appearances from Douglas McFerran (Birds Of A Feather), Tracey Childs (Howards’ Way), Lucy Benjamin (Press Gang, EastEnders), Barry Jackson (Midsomer Murders), Tenniel Evans (Z Cars), Leslie Phillips (Carry On… films), John Michie (Taggart), Kris Marshall (Death In Paradise), Nadim Sawalha (Dangerfield) and Freddie Jones (Emmerdale).