Season twenty-one, which again had John Nathan-Turner as producer and Eric Saward as script editor throughout, continued the previous year's theme of drawing on popular elements from the series' past. These included Davros and the Daleks in a revamped version of the story postponed due to industrial action; the Master; and, rather more surprisingly, two related monster races that had both made their debuts over ten years earlier during the era of the third Doctor...
Peter Davison, recalling advice he had received from Patrick Troughton that three years was the optimum length of time to play the Doctor, had decided at the end of season twenty that he would quit the series at the end of season twenty-one. In subsequent discussions he had indicated to John Nathan-Turner that he might, after all, be prepared to stay on for a fourth season, but this change of heart had come too late as action had already been put in hand to write him out. His imminent departure was announced in late July 1983 and, like his appointment to the role, even received coverage on the BBC's main evening news programme.
Nathan-Turner had decided to break with recent precedent by making the new Doctor's debut story the last of the current season, rather than the first of the next. The main aim of this was to engage viewers' interest in the newcomer and so maintain their loyalty over the between-seasons break.
Somewhat at odds with this, however, was the decision then taken by the production team to make the sixth Doctor unstable and, at least initially, unlikeable - an approach they adopted partly in order to keep their options open as to how the character would be portrayed in the longer term. So ended a season that had seen Doctor Who going through a number of significant developments - although arguably none as significant as those that lay in store during the remainder of the sixth Doctor's era.