There is now only one left of the original Unsolved Crime and Open Case Squad: Gerry Standing, portrayed by Dennis Waterman. The rest of the team have changed – even the leader, the ambitious DS Sandra Pullman (Amanda Redman), left in the last series, replaced by DCI Sasha Miller, played by Tamzin Outhwaite. The other squad members are Steve McAndrew (Denis Lawson) and Dan Griffin (Nicholas Lyndhurst).
Family ties affect both Gerry Standing and Sasha Miller. While Sasha is forced to work with ex-husband Ned as he fills in for Strickland, Gerry returns to his roots in Bermondsey to help arrange his daughter's wedding. As a consequence he is thrown into a case involving the possible murder of an architecture student who is also the grandson of an old friend. Meanwhile, Danny Griffin has been on an FBI course in reading body language.
The team investigate the unsolved killing of brilliant young doctor Lydia Dryden in a case that takes them into the two very different worlds of public and private medicine. Danny Griffin is bereft when daughter Holly leaves home to start university, so his UCOS colleagues throw some fun distractions his way. And he might even be about to acquire a pet...
The team looks into the death of a terrorist 30 years previously after his daughter receives an anonymous note claiming he was murdered - an investigation that takes them right back to the Greenham Common anti-nuclear protests. Meanwhile, Sasha agrees to go for dinner with her ex-husband Ned, which he is hoping will lead to a reconciliation.
When Steve McAndrew's teenage son Stewie is arrested for drug possession, he finds himself face to face again with his ex-wife Tricia as they try to save the boy from a downward spiral. And after a distressed dementia patient escapes her care home to report a murder, the team look into the disappearance of a policeman, possibly murdered but missing since 1956...
Tension mounts as Ned and Sasha are forced to work together when the body of a film critic found in a sewer is thought to be linked to the 20-year-old murder of a concept artist, David Straka. As the team interview Straka's contemporaries, groupies and assistants, looking for possible connections between the deaths, they find themselves immersed in the macabre world of the occult. And Griffin's expert knowledge of the history of London and in particular the hidden Fleet River, proves invaluable.
The team investigate the death of a personal trainer who had belonged to a Roman reenactment society and discover a gang selling illegal steroids, but the motive for murder may not be all it seems. And Danny Griffin starts to become attracted to his forensic pathologist colleague Fiona Kennedy just as he receives some troubling news about his wife.
UCOS want to talk to a Turkish girl who is found working illegally in Dalston, regarding a unsolved murder from 2009. The landlord of a pub, Richard Gibson, died in a fire and the case had remained unresolved. The team meet the landlady of the pub, Joanna Gibson, who is also Richard's widow. His best friend, David is also someone of interest, especially when the team find out the French champagne he is selling, is actually sparkling wine produced in Britain. Sasha enters the team into a 5-a-side football competition.
While investigating the murder of 55 year-old interpreter Agnes Bradley, the UCOS team get a partial DNA match from a teenage boy who once threw a brick onto a motorway as a dare. They interview the boy to see if one of his male relations could be the murderer, only to discover that his mother was raped and they could be looking for a rapist-turned-murderer. Agnes was a chess enthusiast so Gerry Standing and Steve McAndrew interview members of her local club while Sasha Miller and Strickland investigate leads from Agnes’s working life, where they meet a Chilean diplomat with a possible axe to grind. Steve McAndrew’s elderly father is dying, so he brings him to a London hospice for his last days.
When cold-crime enthusiast Ellen Barker is murdered, a photo of Dan Griffin is found at her house. Griffin is interviewed by the murder team, who realise that Ellen was a friend of his. The senior investigating officer assigned to Ellen’s murder investigation is DCI Grace Mackie, one of Sasha Miller’s contemporaries from their Hendon training. Griffin is convinced that the last case Ellen was looking at could lead to her killer, and heads to Minchampton, where a woman called Sally Tunstall was murdered 25 years ago by local lad Dougie Haynes.
A mix tape from 1983 is discovered, containing the voice of a teenage girl who was murdered shortly after it went into her school's time capsule. Griffin becomes convinced that the girl is reading from a speech secretly prepared for the Queen to broadcast in the event of a nuclear war. Meanwhile Sasha is distracted by a romantic entanglement with a charming record shop owner and Gerry is dreading his future son-in-law Robin's stag night, which promises to be something very special...