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.

The team are called in to reinvestigate the disappearance of PE teacher Jason Bowe after a body is found on the perimeter of the elite public boarding school where he was employed. The investigation has come at a really bad time for the school, which is getting to welcome a former pupil, the Rt Hon Geoffrey Parkes MP, for the opening of a new computer centre.

DS Pullman breaks the rules to explore a possible cover-up at the Foreign Office.

Retired DI Steve McAndrew from Glasgow joins the team to reopen one of his old cases when the DNA of a woman who went missing as a teen turns up at the scene of a petrol station robbery.

The team become concerned that undercover police operations may have been compromised when the body of a computer expert who worked with the Met turns up under a false name at a teaching hospital.

The team investigate the death of a 16-year-old tennis star who fell—or was pushed—from a penthouse balcony after she lost an important match to a rival.

The team investigate the murder of an East German immigrant, but they only have his mysterious final words to work with. As they attempt to piece together his remarkable story, Sandra attempts to gain the trust of his estranged daughter.

McAndrew and Standing are sent to Scotland by Strickland for a week, to help the Glasgow Police try and establish a new UCOS section led by DCI Fiona MacDougall. While there, they end up being caught up in a cold case from 1993 featuring the murder of bookie James Soutar.

Thirty years ago, Strickland and a group of his associates, including Stephen Fisher, were involved in a covert operation on behalf of MI5. Now, someone is trying to kill all the members of that group and Strickland turns to the UCOS team for help.