The team reinvestigates the Fifties murder of Frederick Tully, a young wages clerk at Battersea Power Station. Patrick Dunne was hanged for Tully's murder, but his granddaughter, Hannah, is waging a campaign to have Dunne posthumously pardoned.
The discovery of a suitcase containing used fivers in the attic of the Tully home sheds new light on the case, revealing a possible blackmail plot. And when Sir Edward Chambers, the key witness against Dunne, retracts his evidence, the team has reason to question the original investigation. However, with Hannah reluctant to co-operate with the police, it is left to Gerry Standing to charm her mother, June, in order to gain an insight into the case, which Standing takes a little too literally.