The series focuses on the work of the Unsolved Crime and Open Case Squad (UCOS) – a fictional division within London's Metropolitan Police Service tasked with re-investigating unsolved crimes. UCOS primarily functioned with a senior police detective overseeing the work of three retired police officers who would handle each case, and who could bring in police support when needed. Each episode focuses on a different investigation, with characters often coping with problems at their age but using their wisdom to overcome hurdles in the original investigation of cold cases. Both creators, McCrery and Mitchell, devised the title of the programme around the proverb "".