Brian finds the library card of cold case victim Dr Richard Symes, leading him to reinvestigate the death of the professor, who died after falling from the roof of his college three years previously. Sandra and Gerry interview Symes' widow, who believes principal Jeremy Ventham drove her husband to suicide following a conflict over teaching methods.

After being released from jail, notorious paedophile John Davies admits to the abduction and murder of a child 25 years previously. Suspicious of his motives, the detectives reopen the unsolved case in an unusual attempt to prove his innocence, reinvestigating the boy's disappearance while on a demonstration with his left-wing activist parents. Guest starring Adrian Schiller (Being Human) and Samantha Bond (Outnumbered)

A recent rape is linked to two similar attacks at a chocolate factory 10 years previously, leaving the team no choice but to reopen all three cases. The detectives uncover news of an unhappy workforce, learning of an alleged suicide, and their investigation becomes even more complicated when they discover a severed finger was found in one of the company's snacks. After a visit to the doctor, Gerry decides to quit smoking, and instead of resorting to nicotine patches or gum, he enlists Sandra to help him quit

When graffiti appears around London by an unknown person claiming to have murdered a celebrated street artist, the team reopens the four-year-old case. Originally part of a gang, the victim went solo when he received support from a wealthy art patron, leaving the detectives suspicious of his resentful former crew members. Meanwhile, Brian signs up to Twitter to chart the gritty life of a lawman, much to his colleagues' displeasure.

When a retrospective exhibition of murdered fashion designer Ritchie Levene's work opens, the team is prompted to re-examine the three-year-old crime. The detectives learn about his tempestuous relationships with his new spouse, personal assistant and ex-wife Sarah, who believes his brother Adrian is the killer because he had the most to gain from his death. Meanwhile, Gerry enlists Emily to help update his image, although not everyone is impressed with the results.

UCOS reopen the case of a fire at Ealing's Union Club club in which a notorious criminal was killed in 1996. New evidence provided suggests that a serial arsonist is at large and that the killing of gang leader Mark Johnson may have been accidental.

When 18-year-old debutante Barbara Linden-Warner disappeared without trace 27 years ago, the assumption at the time was that she had been kidnapped and her father, a wealthy British arms manufacturer, paid a ransom for her return. When new evidence emerges about her last movements, the indication is that she may still be alive.

When the gun used to murder a talented young boxer 11 years ago surfaces in an armed robbery, UCOS are drawn into the darker side of professional boxing in a case that causes conflict and friction among the team.

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.