Gerry attempts to clear his name before his enemies catch up with him. Sasha and Steve get Fiona's help to examine the evidence against the clock. Danny takes Gerry on the run as they look for the proof they need to prove his innocence.

Jack announces that he he has decided to leave the team, but before Sandra, Brian and Gerry can question his reasons, Whitehall figure Stephen Fisher shows up with one of his secret cases featuring the unsolved murder of a woman dating back around a hundred years. With only 24 hours to solve it, the team attempt to find time to get to the bottom of Jack's surprising decision and attempt to persuade him not to leave.

Pullman seizes the chance to solve a murder that she believes is linked to her first ever case, and the team start putting together a jigsaw puzzle of suspects from a photograph taken in a London park in the 90s. Eventually faced with increasing pressure to hand over the investigation, Sandra makes a huge decision, which is going to change UCOS forever.

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.

The team reinvestigate the disappearance of two young political activists.

Gerry feels spooked following the discovery of UCOS's latest victim, a policeman, whose body has lain untouched under a basement for the last 30 years. Accusations of police corruption and underhand dealings start to surface causing Gerry to face up to some skeletons in his own closet.

Pullman struggles to keep the boys in line as their chequered pasts begin to be revealed. Halford is determined to nail a vicious criminal who has so far eluded him and in doing so he puts himself in grave danger. Standing receives a surprise visitor which shocks him. Pullman is increasingly frustrated and weighs up an opportunity that could end her time in UCOS.

The team reinvestigate a 30-year-old safety deposit robbery, and they soon find themselves being drawn into a case involving police corruption that threatens the future of the UCOS itself.

The team unlock over three decades of secrets and lies on the Rock of Gibraltar and find the link which solves the murder of a playboy shipping heir from '98 and a young local boy from '82. With both cases solved, they return to England where Lane faces a disciplinary hearing, dragging up a death in custody from his past which threatens his career in UCOS.

As Lane comes to terms with life after UCOS, Esther asks him to help one of her book club friends find her missing brother - but will his nose for the truth get him into further trouble? And how will his former colleagues cope without their most dogged sleuth?

The Home Office pathologist asks the team to identify the remains of an unidentified woman, whose remains were found back in 1987. These remains are the only body that he was unable to identify. With his help and that of his attractive assistant, not only must the team identify the body bits, but how she died and who killed her.

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.

Brian Lane enters rehab to treat his alcoholism, but the rest of the team soon join him.

As the series comes to an end, the desiccated, neatly carved-up body of a butcher who disappeared more than 30 years ago is discovered, leading Sandra Pullman and her boys to pay a visit to Smithfield meat market in London, the original murder scene. It's a pity the butcher is dead, because he has a few questions to answer about why the body of a doctor was found hanging from a meat hook all those years ago at the back of his market stall. It's an episode peppered with revelations. We discover Gerry Standing's very interesting family history - he's descended from French Huguenots and is thus tormented by his colleagues for being a fake cockney, much to his annoyance: "Je suis ang-bleedingglais!" he protests. But it's Sandra who has to face up to a startling personal disclosure that has a direct bearing on the case and also throws a whole new light on her father. For once Gerry, Brian and Jack are left completely speechless.

A woman is sent anonymous emails from someone claiming to know what happened to her husband Phillip Mackenna, a prominent scientist working on cold fusion who disappeared while on a train to Paris. As the team investigate, DAC Strickland receives a warning from Whitehall.

The vicious criminal Chopper Hadley, who has been back in the country for a week, is searched for by the team. However, Halford is viciously intimidated and the squad start to realise the full danger of their target. Desperate measures are used and Brian is sent undercover to get Hadley once and for all.

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.

The UCOS team investigate the murder of a young peace protestor, killed at the outskirts of a nuclear base in 1984, and realise that they may be in danger of exposing a Special Branch cover up.

In an attempt to make contact with his late wife Mary, Jack goes to see a clairvoyant. Instead he meets a girl who died in a shipping container in 1982 and has the case re-opened.

The team re-examine the case of Hannah Taylor who was kidnapped from her home in 1992. A body, previously thought to be Hannah's, has just been identified as that of another kidnap victim

When a serial dog killer starts stalking local parks, the team are reluctantly forced into taking on the case.

New series of the drama featuring an eccentric group of ex-police officers brought out of retirement to investigate unsolved crimes. Jack confronts his nemesis in court when Ricky Hanson stands trial for his attempted murder, and Gerry faces the consequences of lying to his 'daughter', Emily. The team uncover a shady organ-donor racket when they reinvestigate the murder of a wealthy businessman who left a three million pound fortune to a prostitute.

The team return to the 1992 case of actor Michael Austin, shot dead by his wife on stage during the opening night performance of Death at the Masked Ball. Already a man down when Halford goes AWOL, the case looks like claiming another member of the team as Lane embraces his newfound love of acting and the theatre.

The team reinvestigates the murder of a popular DJ who died live on air after an arson attack at 80s music station Roxy Radio. Lane is determined to find the missing Jack Halford when Pullman and Standing threaten to quit rather than work with a new team member.