County of Essex
I was convinced at one point that she was going to have been a future-Clara that will have had lost her mind for some reason, and become obsessed with the Doctor.The Masters back story is rather complex, as technically this must be a reincarnation (and not regeneration) of the Master as the original Master had run out of life cycles.
Mistress was a bit of a letdown, but I enjoy how the actress is playing the role. The Master has to be a bit wacko (it's in his back story, after all), and she does that really well.
Ep. 1 was pretty good, but [Moffat biases aside] I thought the moral dilemma they set up for Ep. 2 was a bit too obvious and forced for my taste.
It may go someone to explaining why the "new" Master is a total loon whilst both Delgardo and Ainley were not (and for the record Delgaro is how I judge all Masters).