Season 13, ep 23, February 1976. Fourth Doctor
Not to be confused with the Seeds of Death episode from some years prior.
All the usual Who tropes, this one in particular has so many old white men it’s hard to keep track of them (at least the psychopathic killer had a goatee). 6 episodes means longer than most stories from this season (13), and there’s an excessive amount of quips in the denouement. Just like Ark in Space was Alien 4 years before Alien, this was The Thing 6 years before The Thing (but 23 years after The Thing From Another World)
Next episode – season 14 The Masque of Mandragora