Disclaimer: this is a work of fiction.
Part Sixteen: The Multi-Doctor Era
Between seasons 34 and 35, Paul McGann first raised the possibility of leaving Doctor Who at the end of his third season (season 35), but at the same time raised the question of whether or not it would be possible for him to return to the role in the future - not as a one-off guest-artist as had been done on occasion, as with Patrick Troughton in Two Doctors, but for entire serials or seasons at a time.
Segal was against this idea at first, fearing the loss of a strong leading man from the show, but was persuaded by his writing team that it could work if, instead of regenerating the Doctor into someone new, they could persuade the old Doctors to make return appearances, giving the production team golden opportunities for publicity. Tom Baker, Peter Davison, Colin Baker and Sylvester McCoy were all sounded out about this. Tom Baker refused outright. The others all provisionally agreed, depending on other commitments they might have at the time.
One of Segal’s last actions as Producer was to approve this ‘multi-Doctor’ direction for the show. He then resigned from his position and was succeeded by Gary Russell, another long-term fan of the series who had been Editor of Doctor Who Magazine for several years.
Stories starring ‘past’ Doctors were originally intended to be classified as ‘Missing Adventures’ and designed to fit in with the style and timing of the Doctor-in-question’s original era. Though popular among the writers (most of whom were fans of certain previous eras and so delighted at the chance to write for them), this idea was impractical from a production point of view, not to mention the logistical headache of scheduling the actors to play the right Companions for the eras.
At a writers’ brainstorming session, a sci-fi explanation for the presence of previous Doctors in the ‘present’ was devised, and an overarching story was contrived to tie the different serials together into a coherent, thematic, whole. At the core of Doctor Who is the idea of time-travel, and this was exploited in a way that has rarely been seen in the series before or since.