The eighth season was to see Doctor Who coming in for renewed criticism from certain quarters - particularly the media, although questions were also asked in the House of Lords - over the level of horror and violence contained in its stories. This was somewhat ironic, given that the previous season had actually been rather more adult in tone and had attracted no such odium.
New producer Barry Letts, working closely with script editor Terrance Dicks, was keen to steer the series back more toward its family viewing roots, feeling that under the new format introduced by his predecessors it had become too focused on hard-edged science-fiction and military action at the expense of the lighter, fantasy-based entertainment and warm, identifiable characters that it had featured in the past.
It was with this in mind that the two men introduced in place of Liz Shaw a new companion character - Jo Grant, an impetuous teenager assigned to UNIT (originally planned to be a UNIT lieutenant) as a result of some string pulling by an influential relative - who was much more akin to the old-style companions. They also decided to give the Brigadier a new second-in-command more suited to his status than the relatively lowly Sergeant Benton (who would nevertheless continue as a regular). This was Captain Yates, who was envisaged also as a possible love interest for Jo - although, in the event, little came of this in the transmitted stories. Thus was formed the basis of what would eventually come to be referred to by fans as the 'UNIT family'.
Another, arguably even more significant innovation at this point was the introduction of a new regular villain in the person of the Master - a renegade Time Lord dedicated to evil - whose relationship to the Doctor would be similar to that of Moriarty to Sherlock Holmes. Indeed, so taken were Letts and Dicks with this character that they decided to have him appearing as the Doctor's adversary in all five of the eighth season's stories - an occurrence that was to remain unparalleled in the series' history.
Season eight can be seen as having provided a template for the remainder of the third Doctor's era. Barry Letts and Terrance Dicks had succeeded in their aim of taking Doctor Who back into family viewing territory, and the gritty realism of the previous year's stories had consequently given way to a lighter, more fantasy-based style. UNIT continued to constitute an important element in the format, but characterisation and humour now took precedence over military hardware and action set-pieces.
There had also been established a group of reassuringly familiar regular characters - the Doctor, the Master, the Brigadier, Jo, Yates and Benton - and the actors who portrayed them had bonded together into a highly effective team, their affection and respect for each other clearly evident from the transmitted episodes. All these developments would be carried forward and built upon in the seasons that followed.