By the end of 1966, Doctor Who was well on its way to becoming a much-loved national institution, although its popularity had declined somewhat since the peak of the second season. The process of change initiated by new producer Innes Lloyd and his story editor Gerry Davis during the latter part of the third season would continue during the fourth, facilitated by a general relaxation of the restrictions placed on the series by their BBC superiors.
Thus they encountered no apparent objection to their introduction, in the person of Ben, of a companion with a Cockney accent - a move that only a few months earlier had been vetoed in the case of Dodo - and were able to drop the historical story type, which had originally been seen as an integral part of the series' format. And whereas the then Head of Serials Gerald Savory had overruled John Wiles when he had thought to write out William Hartnell and introduce a new Doctor, his successor Shaun Sutton proved much more willing to go along with this idea.
When the fourth season got under way, however, viewers could scarcely have suspected that in just a few weeks' time Doctor Who would have a new lead actor. At this point, the series appeared much the same as ever as Hartnell's Doctor embarked on another adventure in history with his new companions Polly and Ben.
Gerry Davis's departure from the post of story editor around the end of April 1967 brought to a close a period of relative stability for Doctor Who's production team. It also marked the end of Kit Pedler's regular involvement as the series' unofficial scientific adviser (although he would continue to provide storylines for Cyberman adventures throughout the remainder of the second Doctor's era). Innes Lloyd was also keen to move on by this stage, feeling that he had contributed all he could to the series, but remained as producer for the time being as no suitable successor was available; Davis had in fact been invited to take over from him, but had declined.
The new story editor appointed to the series was former actor and radio writer, director and producer Peter Bryant, who had been trailing Davis as an assistant since around mid-January 1967. Bryant was also seen as a potential replacement for Lloyd; indeed it had been thought initially that he would take the role of associate producer on the series, hence his credit as such on The Faceless Ones. Around the time that he took over from Davis, Bryant also brought in a new assistant of his own, namely writer and sometime actor Victor Pemberton (who had actually appeared in The Moonbase as one of the base personnel).
The fourth season had been, all things considered, a successful one for Doctor Who. A critical change of lead actor had been well accomplished; a period of experimentation had led to the development of an effective new format; and, with the arrival of Jamie in The Highlanders and Victoria in The Evil of the Daleks, two promising new companion characters had been introduced in place of Polly and Ben. The changes overseen by Lloyd and Davis had, in short, revitalised the series. The task facing Lloyd and Bryant for the fifth season was to consolidate and build upon that success.