DC Frank Craven is more of a "get up and let's 'ave him" kind of cop, not afraid to push himself amongst the action and get involved when he is required to. Frank is regularly partnered with Stone, and the pair seem to have a good working relationship. Craven was initially designed to feature in a minor role, assisting Stone with the mathematical equations in "The Critical Path". However, after Tim Dantay left the series, Craven's role was heavily increased, with scenes for "The Critical Path" re-filmed and the scripts for the remaining three episodes re-written to replace Simner with Craven. Craven does not appear in "Happy Families" or "Mr. Right", despite these being midway through the first series, however this was due to the episodes being broadcast out of initial production order.