Season 4

The future of the team is threatened and without having that to deal with, Sandra has to take drastic measures to prevent Jack from exacting revenge against the man who killed his wife Mary. Sandra also has the added benefit of trying to keep Jack’s actions from shady new recruit DCI Karen Hardwick while working on a 10-year-old murder case.

Sandra's private and professional worlds become intertwined when her mother has a fall and goes into a care home - but the establishment is revealed to be a scene of a suspicious death a year earlier.

When an armoured van is discovered at the bottom of a lake, the team makes a link with the murder of a women 17 years ago.

A family feud erupts when a rich and lonely old woman, Dorothy Hepple, is found dead in her home. Dorothy leaves all her money and property to her beloved cats, rather than her nephew, Harry, and niece, Caroline. Her body lay undiscovered for two weeks and the cause of death is undetermined, but the fact that her cats were deliberately locked in the house, forcing them to start eating their owner's remains and any evidence, makes Jack suspicious. There appears to have been no love lost between the late Ms Hepple and her neighbour, Tim Cuswell. Meanwhile her carer, Dale , seems to have been devoted to her, his motives are questionable. When the last of Dorothy's feline beneficiaries dies, her estate suddenly comes up for grabs. With no shortage of people laying claim to the estate, the team decides to reopen the investigation into Dorothy's death.

The team reinvestigates the 1950s murder of a young wages clerk at Battersea Power Station. Richard Dunne was hanged for Frederick Tully's murder, but his granddaughter, Hannah, is waging a campaign to have Dunne posthumously pardoned. The discovery of a suitcase containing used fivers in the attic of the Tully home sheds new light on the case, revealing a possible blackmail plot. A trace on the used fivers reveals that they should have been destroyed in the Battersea Power Station furnaces back in the 1950s, but were actually being saved by Douglas Murray, a friend of Tully's. It also becomes clear that the Battersea furnaces were being used to destroy other sensitive documents as well as used bank notes. When the team discovers a classified document relating to a massacre of civilians carried out by the British Army in Kenya, they uncover a blackmail plot spanning more than 50 years.

When Brian's dog finds a body, it prompts two people to confess to murder. It turns out that the body is over 600 years old, so Sandra, Jack, Brian and Gerry must discover why the pair took responsibility for a crime they couldn't possibly have committed and if they are the perpetrators of other killings. Elsewhere, Strickland is rather keen for them to solve an even more tricky mystery that is closer to home.

When a camera and film belonging to a photographic lab assistant murdered in 1987 are found in a Soho pub toilet, the team reopen a 20-year-old case. Elsewhere, Gerry is less than happy when his daughter Emily joins the team and looks to Sandra as a role model.

The news that Sandra's father, a DI, killed himself while under investigation for corruption, throws into doubt everything she believed in. Her mother, Grace , is in hospital following a stroke, and she wastes no time in confronting her, but she doesn't get the answers she's looking for. Unfortunately, her father's service records provide Pullman with some revelations she may never come to terms with. Meanwhile, Christy Berlin asks the team to look into the death of the man she's recently discovered was her biological father - ringmaster The Great Miraculob. But will the investigation at Spingles Circus be enough to distract Sandra from feeling betrayed by her colleagues?