DCI Sasha Miller leads a team of detectives called out of retirement to solve cold cases. Season Twelve sees the departure of the last-remaining original member of the Unsolved Crime and Open Case Squad, Gerry Standing, who is replaced by old-school ex-copper Ted Case.

The old dogs of the Unsolved Crime and Open Case Squad are about to welcome a few new faces, but first, Detective Superintendent Sandra Pullman and her loyal team, Gerry Standing, Brian Lane, and Steve McAndrew, will solve their final cases together, bringing justice to decades-old murders that stumped London's Metropolitan Police.