Quite a few things to unpick in tonight's episode.
First off, the Master can't possibly be dead, and I suspect he used the same trick that he (evidently) did in "Death in Heaven" back when he was Missy.
It was a good climax, but it reminded me of the denouement of "The Poison Sky" back in series 4 - basically another character sacrificing themself in the Doctor's place when she went on a suicide mission.
Secondly, the big reveal is that apparently the Doctor had many different incarnations before she/he became William Hartell, but started off as female. And this series' new incarnation possibly fitted in sometime before William Hartnell - the episode didn't make it clear.
Another thought I had - maybe the fact that the Doctor didn't seem to remember the incident with himself in the barn with Clara in "Listen" might be because he'd forgotten a lot of his childhood, consciously at least, and only had dreams about the incident.
So, as I understood it, the Irish policeman was the Doctor? It seemed that way.
Or, it could be that Moffatt and Chibnall constantly re-writing the Doctor's backstory is becoming too convoluted, a bit like what the writers of Once Upon a Time did with its characters (certainly by the time it reached Season 4).
They did a good explanation at least of how the Lone Cyberman ended up back in Mary Shelley's time.
As for the ending, it made a good cliffhanger - a recall to the way Russell T. Davies ended many of his series.
Could Captain Jack Harkness appearing in the montage of former Doctors be another subtle clue to something? (Hopefully not, I don't think he's the Doctor).
So, here is my usual poll - my favourite episode is Spyfall (Part One) this series because of the big reveal.
Least favourite is hard because this was a good series - I'll go for the Nikla Tesla one; it was the most filler-like.
I hope someone other than me will do the poll this time.