“I’m afraid, like Mr. Wells, the Doctor has a vivid imagination.” – Lady Cranleigh
This story is famous for being one of the only “pure” historicals after those kinds of stories were ended in the Troughton era. The problem with considering it such is that the whole point is that we are to presume that this is in fact not a historical. The story wants us to watch this foray into history constantly wondering when the alien monster is going to appear. Thus it can sustain this tension with the unseen heavy breathing figure hidden in the walls and several other red herrings (like the people involved seeming to already know of the Doctor, mentions of the Master). It’s not quite the same as First and Second Doctor’s simply being swept up in historical events.
The story starts with a bit of a mystery vibe as we open in the middle of a murder. The sudden sight of a South American native sitting at a table reading a book just seems surreal. For a time, however, the story itself becomes unimportant and the whole first episode turns out to be just a fun romp where the TARDIS crew gets to let loose—from the Doctor showing off his prodigious cricket skills to the Tegan and Nyssa dancing it up. It’s actually nice to get to see them seem to relax a bit. Adric even looks more normal after getting out of his Alzarian garb. (The actors are obviously having fun too—it’s neat to see Sarah Sutton put such a unique spin on Nyssa’s doppelganger.)
The second half of the story goes a bit off the rails. There’s definitely a sense of frustration as we the audience know the Doctor is telling the truth and yet every revelation undercuts his believability, but the scenes of the arrest and them taking the Doctor and crew to the police station become ridiculous. The whole thing is revealed and ended rather abruptly such that the danger hardly has time to settle in before the episode is over. A rather inconsequential story over all.
Best (or worst) unsettling moment:
The disfigurement of George Cranleigh’s face is rather extreme to see (and even more so when it’s explained they cut out his tongue too.). Funnily enough, I find the house burning to cause me more apprehension than Nyssa’s kidnapping. I keep wanting to yell to someone to hurry and put out the fire!
How is it that Nyssa has an Earthling double? We can usually explain this away as an human ancestor (like Steven) but we’ve already been shown that Nyssa’s world is contemporary with 1980s earth. The other doubles we’ve seen have been those apparently “copied” by Time Lords. Could there be any such connection for Nyssa? One wild theory could be that before arriving as the Melkur, the Master had to first genetically alter Tremas in the past to make his DNA more Gallifreyan so he would then be able to merge with him in the future. These genetics would have been passed on to Nyssa making her partially a Time Lord, including the trait of her appearance taking on that of a random individual in the universe.
Unfortunately, there are some scenes that really stretch or even break believability in the second half of the story. It makes no sense that the Doctor would let in a bunch of policemen to the TARDIS to prove the story of his innocence. And it makes even less sense that they would simply be surprised and impressed with the TARDIS like he had shown them some cool new sports car or something. They should be absolutely freaked out. When the Doctor travels with them back to the mansion and they just accept it without much thought, it defies credibility.