Doctor Who hints at big new mystery – what is the Doctor’s lie?

In the climactic final moments of the episode, the Doctor learns that old ally O (Sacha Dhawan) is actually her arch-foe The Master, who has been working with the unnamed aliens for unknown reasons. Trapping her friends in a plummeting plane and zapping the Doctor to a creepy alternate dimension, The Master signs off by dropping a truth bomb on his fellow Time Lord, which hints at a new arc for the series as a whole.

“One last thing, something you should know in the second before you die,” Dhawan’s Master says.

“Everything you think you know is a lie.”

So what on Earth (or Gallifrey) could this mean? Considering it’s directed at the Doctor, not Yaz/Ryan/Graham, it seems unlikely to be another attempt by the Master to undermine their trust in their time-travelling pal (as he did with Graham earlier in the episode).

Instead, this seems to tie into something the Doctor believes about herself or the world, and we’re racking our brains to think what it could all be about – though given the pair’s shared heritage, it makes sense to assume this might be related to some Time Lord secrets.

Could it be that rumours of the new series revealing the Doctor has had more former incarnations than we realise – including some other women – will come true after all? Or is it something to do with a secret rot at the heart of Gallifrey (beyond, you know, all the not-so-secret rots the Doctor has already discovered in the past).

Alternatively, it could be that these things the Doctor “knows” are about her own character and background. The Doctor knows she’s a hero, who threw off the shackles of the stuffy Time Lords to travel the universe helping people – but what if there’s more to the story than she realises? Has someone else secretly been pulling her strings for 2000 years? And if so, what would they be getting out of it?

Or could this whole thing actually relate back to the Timeless Child mystery established in the last series? Showrunner Chris Chibnall has hinted that this arc will be picked up again in the new series, after all, and it did seem like that this mystery might relate to the Doctor’s past…

“We see deeper though, further back,” the evil Remnants whispered to Whittaker’s Doctor in series 11's second episode, The Ghost Monument.

“The Timeless Child… we see what’s hidden, even from yourself. The outcast, abandoned and unknown…”

Hidden, even from yourself? Sounds a lot like “everything you think you know is a lie” – and if these two mysteries are related, it could be that either the Doctor or the Master are the Timeless Child themselves.

Unless of course, it’s something else entirely – and until we learn more, for now we’ll have to rely on Jodie Whittaker’s assurances that this mystery will continue as the series goes on.

“The questions will keep coming!" she teased at a recent screening of the episode.

Hopefully, a few answers will be tailing them close behind…

Doctor Who continues on BBC One on Sundays