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.

The OAP detectives return to investigate a fresh batch of unsolved crimes, beginning with the murder of a palaeontologist at the Natural History Museum. After a bit of digging, the team discover the victim was a respected but outspoken scientist with a knack for rubbing people up the wrong way - and when they discover he was strongly opposed to the museum's sponsorship deal with a large fuel company, the old dogs soon have plenty of suspects.

Amanda Redman stars, with guest appearances from the late Trevor Bannister (Are You Being Served?), Lucy Brown (Primeval) and Natasha Little (Spooks)