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.

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.

Following the 1997 General Election Ben Ransley, a young researcher for successful MP Liz Jackson, was murdered and the case is reopened on the discovery of £40,000 in an off-shore account in his name. Ben's best friend, arrogant lobbyist Eddie Trenton, gives Sandra a photo of Ben with his girlfriend, who turns out to be Hana, the Bosnian wife of tycoon Peter Russell, and she also disappeared in 1997. French policeman and former war crimes prosecutor Max Clement comes to London and tracks down Hana, whose whole family was killed in the Bosnian war. Hana believes Ben, with whom she was set to elope, was killed by the man who got her to England and introduced her to Peter but Dan discovers that Ben was in a position to leak information about a government arms deal, which would have been injurious to certain people. This solves the case.