10 Biggest Doctor Who Retcons

During the 12th Doctor's tenure we were introduced to Missy, the first female incarnation of iconic arch-enemy The Master. Missy was a fan favourite thanks to Michelle Gomez' delightfully loopy portrayal and Steven Moffat's clever writing. More morally ambiguous than many of her predecessors, Missy underwent a unique character arc as she attempted to become "good" and redeem herself of her past misdeeds.

This culminated in the sublime Series 10 finale The Doctor Falls, as Missy and her previous incarnation (played by John Simm) faced off, killing one another in the process. This seemed like the perfect ending for the character of the Master as a whole, as they revolted against the embodiment of their own troubled past.

Just over a dozen episodes later however, the Master returns in the form of Sacha Dhawan, and he's as evil as ever. It's as if Missy's redemption never happened. Arguably, the Master defaulting back to his wicked ways was inevitable, but this feels way too soon, and especially for fans of Missy it's an upsetting retcon. It would be better if Missy's attempts to change her ways were acknowledged at all by the Doctor or the Master. Just a single mention of Missy would've been enough to establish a sense of continuity, but as it stands her excellent character arc seems to have been entirely forgotten.