It's fair to say that the twelfth series of 'Doctor Who' gave us more questions than answers. That's not an accident - current series showrunner Chris Chibnall spoke of having a multi-year plan when he accepted the job, and he's barely over halfway through executing it. We got a lot of revelations and new information by the time 'The Timeless Children' finished the current season, but we've had a few months to consider all of the implications since then. Specifically, we've been thinking about where the mystery female Doctor played by Jo Martin fits into the Doctor's whole timeline.
This would be a good time to look away if you haven’t seen the most recent season of the show yet. We’re about to cover a lot of spoilers.
By the end of ‘The Timeless Children,’ we found out what the Master meant when he warned the Doctor that ‘everything she thought she knew was a lie.' The Doctor is not just another Time Lord. She's not even originally from Gallifrey. She's a lot traveler from elsewhere who slipped through a rift between dimensions and became the template that all Time Lords were based on. She's lived many lives - possibly hundreds of them - only to have all of those memories erased before she became William Hartnell's First Doctor. We know that she worked for the shady Gallifreyan equivalent of the CIA, but we have no idea what she did for them, and neither does she.
The simple explanation for the existence of Jo Martin’s Doctor - first revealed in a mind-bending plot twist toward the end of ‘Fugitive of the Judoon’ - is that she’s one of these past lives. She has no recollection of being Jodie Whittaker’s 13th Doctor, and therefore she can’t be from the future. The 13th Doctor has no memory of being her either, but that could easily be explained away by the mind wipe that took place prior to the beginnings of the series in 1963. We know that Jo Martin isn't playing a false or 'trick' version of the Doctor - that's been explicitly confirmed several times - and so a 'pre-Hartnell' version of the character is the general assumption. Held up to the light, though, that doesn't make much sense.
Firstly, we don’t even know that the Doctor called themselves ‘The Doctor’ prior to the First Doctor’s assumption of that identity. Secondly, Jo Martin’s Doctor has a TARDIS, and it’s shaped like an old London police box. It's an established fact in the 'Doctor Who' canon that the time ship only took on this appearance after its chameleon circuit broke in London during the first-ever serial 'An Unearthly Child.' Prior to that, it blended itself in with the local environment everywhere it went. The mere fact that Jo Martin's Doctor has a police box-shaped TARDIS is evidence that she's not pre-Hartnell at all. She must, therefore, be post-Hartnell.
We’ve seen the show play this trick before when it managed to retrospectively wedge John Hurt’s Doctor in between Paul McGann’s Eighth and Christopher Eccleston’s Ninth, but this is different. The only other time we didn’t directly see the Doctor change from one form to the next is between Patrick Troughton and Jon Pertwee. That could, in theory, allow Jo Martin’s Doctor to exist in that space. There are problems with that idea too, though. Firstly, Martin’s Doctor didn’t recognize the sonic screwdriver, which was already an essential part of the Doctor’s toolkit by the time the Second Doctor’s time ended. Secondly, the 13th Doctor should remember her if that’s where she fits in the narrative. Once again, we have an inexplicable hole.
This is the point where we should remember two things from the show's lure. Firstly, as River Song liked to repeat ad nauseam, 'the Doctor lies.' Secondly, as David Tennant's 10th Doctor remarked to Matt Smith’s 11th in ‘Day of the Doctor,’ regeneration is a lottery. We don’t think that’s quite accurate, though. We think it’s more like an online slots game. The outcome of a lottery is utterly random. You always know roughly what you’ll get when the reels of an online slots game spin on website like RoseSlots.com, you just don’t know what order they’ll land in. An online slots game will always contain all the pieces of the puzzle; you just need to line them up in the right order to get any value out of them. All of the pieces that would give us the secret of Jo Martin’s Doctor are already there; we just need to piece them together and make sense of them.
The Doctor has always been very keen not to pollute an established timeline, especially not their own. Just because Martin's Doctor told Whittaker's 13th that she didn't recognize her doesn't mean she was telling the truth. The fact that she asked what the sonic screwdriver was doesn't mean she didn't actually recognize it. She could simply be trying to protect her predecessor from knowing what comes next before her time. Since Christopher Eccleston left the show, each subsequent Doctor has stayed in the role for three seasons. David Tennant did it. Matt Smith did it. Peter Capaldi did it. Jodie Whittaker's next season will be her third. She's probably going to pass the role on. What if it's already been cast? What if she turns into Jo Martin, and she'll have been hiding in plain sight in front of our eyes since halfway through season 12? That would be an incredible trick to play on viewers, and it would explain the timeline and tidy up the seemingly-fractured continuity at the same time.
The BBC has gone to great lengths to assure us all that Jo Martin is ‘really’ the Doctor. Two appearances in the show that amount to little more than cameos wouldn’t be enough to justify that tag. If she’s the next Doctor, the stance would make a lot more sense. Far from being a continuity error, Jo Martin’s Doctor might well be the 14th. If she is, we’d have to consider that a masterpiece of writing.