The team is less than pleased when arrogant civil servant Stephen Fisher coerces them into investigating the murder - in 1851 - of Abigail Padua, a mathematical expert whose death led to the collapse of her family business and a widespread financial crisis. With no living witnesses and a different geography to the time the team must pore over the original statements to prove that the killer was a witness who lied to the police. However, they, with Strickland's backing, have another mystery on their hands - Fisher's obsession with cracking the case, which itself could have far-reaching effects in the modern business world. Jack however is able to thwart Fisher before he leaves the unit for good to spend his last days in France.

Still missing Jack, the team reopens the disappearance five years earlier of PE teacher Jason Bowe when human remains are found at Peregrine Manor school, where he taught. Of the staff only support worker Helen Hanley is helpful. Stuffy Latin teacher Archie Millgrow argued with Jason about his over-familiarity with pupils whilst former student Eleanor, now the school secretary, and sports jock Oliver believed Jason was having an affair with pupil Melissa. Brian is more concerned that, despite falling intake numbers, school finances are surprisingly healthy and suspects Jason stumbled upon a plot by which wealthy donors subsidised the school in return for favours from old boy Geoffrey Parks, MP, Melissa's father. Then one of the suspects makes a confession but the team is not convinced and believes they are covering for someone else.

At Christmas 2008, Foreign Office employee Annabel Tilson's body was found in a frozen lake, the assumption being that she killed herself after suffering a miscarriage and demotion at work when her lap-top, containing sensitive information, was stolen. Now her twin Minnie has unearthed a video showing that Annabel met somebody prior to her death and was probably murdered. Sandra learns that Annabel was deliberately made a scapegoat to get her out of the way on discovering her married boss's affair with a colleague. She also stumbled on insider information trading, but the key to her death turns out to be her personal, rather than professional life.

In 2003, 17 year old Georgia Wright vanished after a university disco in Scotland. Now traces of her blood are found following a garage raid in London, bringing dogged retired police inspector Steve McAndrew to UCOS to ask them to investigate. CCTV proves that Georgia was not one of the robbers but worked at the garage as a cleaner,,disappearing soon afterwards. They then get a lead in that Shane Morrison,,one of the last people to see Georgia alive, is a fantasist, who persuaded another girl Sophie that he was a secret agent, forcing her to live life on the run with him. The team believes that Morrison is still about and has Georgia in his power. Though the others initially find Steve irritating and his accent incomprehensible, Gerry warms to him over a few whiskeys and, the case over, Sandra has a proposition for him.

Some months after his mysterious disappearance the corpse of young police computer operator Martin Longthorn is smuggled into the morgue at a London teaching hospital. Though he died of an aneurysm the UCOS team are involved as his date Catherine, the last person to see him alive, claims he disappeared suddenly after taking a very important phone call. Investigation of Martin's computer shows he was apparently a member of the Roguenet Group, an organization that hacks into corporate companies and banks to sabotage them. However it turns out that he was actually infiltrating them to unmask their leader Boz, making his death seem more suspicious. Brian, meanwhile, is jealous of Gerry's rapport with Steve, leading to Esther making an effort to rectify the situation.

When junior tennis champion Alice Kemp fell to her death from a balcony in 2010, it was assumed she killed herself as she had lost a crucial match but now a cleaner recalls hearing raised voices just before the death and the case is reopened. Alice's agent, Anthony Marshall, claims he lost a valuable client but admits Alice was considering a change of representation whilst Victoria, Alice's mother, tells the team that David, her estranged husband, a gambling addict, had visited Alice before the fatal match. He admits that he was betting against her for money and asked her to lose the march but denies any foul play. Fawn, the player who beat Alice and took her place as Number One, was nonetheless good friends with her and helps the team find the person responsible for Alice's death though Brian is less successful in trying to get his dog in with a model agency.

Ten years earlier the charred corpse of young poet Sean Doherty was found in the scrapyard of Turkish drug-dealer Mehtin Topal, though Topal was not convicted of the killing. Now the case is reopened and the team interviews Sean's contemporaries, including his tutor and lover Sarah Powell and ex-flatmate Luke Oswald, now a media darling. Unlike cynical Gerry, Brian is taken by the world of poetry but Sean's brother-in-law Eoin also claims that Sean had gangster connections. CCTV provides an unexpected clue to the solution of the case, fuelled by Brian's poetical observations and leading to a surprising discovery.

The team reopen the murder of East German refugee Max Klein, whose last words were 'Blue Flower'. Visiting the site of his death Sandra and Steve meet Grace Cusack, whose son was killed at the same spot a year before Max's death and tells them he came to England to look for his daughter Mia who had escaped East Berlin ahead of him. Meanwhile Gerry and Brian visit a recycling centre where Max worked and learn that he stole bundles of documents but are challenged by arrogant Inspector Rosser, who claims that they could interfere with his investigation of the centre in connection with identity fraud. When Mia is located she denounces her father as a member of the Blue Flower group which was pro-Stasi though ultimately the deaths of Grace's son and Max prove to be related and less political than expected.

Following an attempt to kill Stephen Fisher, Strickland summons the team to a secret meeting. He tells them that thirty years earlier he and Fisher were part of an intelligence group investigating the IRA but their source journalist Simon Bisley was killed in a hit-and-run and the investigation ended. Now others of the group are being murdered. Bisley had linked the IRA to a career criminal Carl Dillon who, according to Gerry's informant Tinker, has just recruited two assassins and a telling document which could incriminate Dillon was stolen from Bisley's office. However Brian believes that a rogue member of the former secret service team has a vested interest in stealing the document and silencing their colleagues over it, giving Strickland the means to go after them though the team is dissatisfied with the result.

Gerry and Steve go to Glasgow, ostensibly to advise on establishing a UCOS office there but are asked to investigate the nineteen year old death of bookmaker James Soutar, given that the investigating officer at the time Frank McNair was suspected of corruption. He was also the man who ran off with Steve's wife. The pair are surprised to learn that Soutar left fifteen thousand pounds to Cathy Sinclair, who claims she never met him, as well as legacies to children's charities. However Charley, Steve's younger girlfriend, tells Gerry that she and Cathy were in care together and that Soutar was involved in a vice ring, grooming girls in care for sex. The duo solve the case and, before returning to London, Gerry helps Steve get his revenge on McNair.