Warning: The following contains SPOILERS for Doctor Who, season 12, episode 2, “Spyfall - Part 2.”

Were The Doctor and The Master among the founders of the Time Lords in Doctor Who? This radical idea was once proposed by the writers of Doctor Who, but the show’s hiatus in 1989 prevented the plotline from being fully enacted. However, a line in the two-part season 12 premiere “Spyfall” suggested that showrunner Chris Chibnall has brought this idea into play once more.

The action of “Spyfall” saw The Doctor and her companions joining forces with a former MI6 alien expert known as “O” to investigate an apparent invasion by strange creatures that were attacking spies associated with every intelligence organization on Earth.  Part 1 of “Spyfall” ended with the stunning revelation that O was really The Master, returned in a new regeneration. The conclusion of “Spyfall” delivered the equally stunning news that The Doctor’s homeworld of Gallifrey had been destroyed and that The Master was responsible.

The Master confessed his crime to The Doctor in a prerecorded message, even as he defended his actions. “I had to make them pay for what I discovered,” The Master claimed. “They lied to us. The founding fathers of Gallifrey. Everything we were told was a lie. We are not who we think. You or I.”

The message seemed fairly straightforward, but The Master rarely does anything in a direct manner. In “Spyfall - Part 1,” for instance, he teased The Doctor regarding his true identity, telling her she had to “look for the spymaster” before revealing himself as “the spy Master.” Considering The Master’s exact words, a question is raised; when he refers to “the founding fathers of Gallifrey” is he referring to the ones who lied to The Doctor and The Master? Or is The Master saying that he and The Doctor are the founding fathers of Gallifrey?

One Of Doctor Who’s Oldest Theories Is About The Doctor Creating The Time Lords

The idea of The Doctor being one of the founders of the Time Lord society was first suggested by script editor Andrew Cartmel, who oversaw the writing of Doctor Who from 1987-1989. With a team of writers (chiefly Ben Aaronovitch and Marc Platt), Cartmel tried to restore the sense of wonder and mystery that many felt had vanished from the show during the 1980s, as more and more stories came to be focused on the Time Lords and Gallifrey. The centerpiece of this effort was a suggestion that The Doctor was hiding some great secret about his past and that he was far more than the renegade Time Lord he claimed to be.

While there was never a formal plan according to Marc Platt, allusions to the truth of The Doctor’s past did make it into various episodes during the final three seasons of the original run of Doctor Who. Unfortunately, very little came of these hints thanks to the interference of the series’ show-runner John Nathan-Turner and his tinkering with the scripts. After Doctor Who went on hiatus, Cartmel, Platt and Aaronovitch passed their notes on Cartmel’s theory on to Peter Darvill-Evans; editor on the New Doctor Who Adventures book line, which was meant to continue the story of the show. The theory was then worked into various novels and dubbed the Cartmel Masterplan by fans of the show.

The ultimate goal of the Cartmel Masterplan was to reveal The Doctor as the reincarnation of The Other; one of the three Time Lords whose work secured Gallifrey’s control of time travel. Little was known about The Other beyond his being a mysterious figure spoken of in the legends of ancient Gallifrey and that he claimed to have come forward in time to help the people of Gallifrey in their time of need. It was said that it was The Other’s mastery of science that ultimately perfected their time-travel technology and led to the development of the first TARDIS. While the mythology of The Other is not officially regarded as canon (BBC’s official policy is that only the television show counts in regards to the history of Doctor Who) other aspects of the Cartmel Masterplan did make it on the air.

How The Cartmel Masterplan Has Been Worked Into Doctor Who

Little of Cartmel’s Masterplan made it into the final three seasons of Doctor Who. The larger part of the references which did make it in were little more than vague hints, with various villains who had previous experience with the Time Lords claiming there was something different about The Doctor. Chief among these were Lady Peinforte in the episode “Silver Nemesis,” who claimed to have knowledge of The Doctor’s actions during the Dark Times of early Gallifrey - a period of time explicitly said to have occurred long before The Doctor was born.

Perhaps the most blatant filmed reference came in “Remembrance of the Daleks,” a story which found the Seventh Doctor recovering an ancient Time Lord artifact called the Hand of Omega whilst coping with the Dalek Civil War coming to Earth. At one point in the story, The Doctor told his companion Ace about the Hand of Omega and how it was a device which the Time Lord Omega used to manipulate stars. “And didn’t we have trouble with the prototype,” The Doctor commented wistfully. When Ace questioned The Doctor on the use of the word “we,” he quickly corrected himself and said “they.”

The final episode of season 26, “Survival,” would have ended with The Master confronting The Doctor over his true past. Unfortunately, when it was determined that “Survival” would be the last episode of the series before it went on hiatus for an unknown length of time, the ending was rewritten so as to not end on such an ambiguous note. Still, the suggestion that The Master and The Doctor had been around far longer than previously suggested was going to be there.

Theory: Doctor Who Season 12 Reveals The Doctor & Master Created The Time Lords

The one certainty about the on-going story of Doctor Who season 12 is that it will center around a being known as the Timeless Child. Considering what we know of Time Lord regeneration and how the only limits on how many times a person can regenerate are imposed by the Time Lord leadership, it is entirely possible, as Cartmel suggested, that certain key figures in Time Lord history were forcibly reincarnated, being reborn into new lives with no memory of who they were. If that’s the case, The Doctor and The Master could have been among the first generation of Time Lords and possess powers far beyond those of the later generations of Time Lords, much like the Time Lord founders Rassilon and Omega. “Time will tell,” as the Seventh Doctor once said. “It always does.”

More: Who Is The Timeless Child? Doctor Who Season 12’s Big Mystery Explained