Dr Shearsmith was a resident of Crook Marsham. He and Jack Prudhoe were the first two people to disappear from the village after the Sentience began to fully manifest in December 1968. (PROSE: Nightshade; AUDIO: Nightshade)
Behind the scenes
Shearsmith is likely a reference to Reece Shearsmith, one of Mark Gatiss' co-creators and co-stars in The League of Gentlemen, whom Gatiss mentions in the afterword to Nightshade. Shearsmith later played Patrick Troughton in the docudrama An Adventure in Space and Time and Gagan Rassmussen in TV: Sleep No More.