S01E06 - The Aztecs
First thing’s first - Jacqeline Hill is just amazing, more amazing than that helmet they make William Russell wear, which is really saying something. Barbara has aswiftly become the standard by which I hold all other companions - especially now that you get to see her at her most flawed.
Probably the most interesting thing about The Aztecs is that the TARDIS crew are kind of the bad guys. Human sacrifices and fights to the death aside, even the devious Tlotoxl is really just trying to preserve his way of life from some admitted imposters.
The Doctor’s main complaint is that Barbara’s playing god interferes with history, but the real problem is an English school teacher is trying to force her views on a society. Even worse, she expects them to accept her changing their whole way of life without complaint (oh, and that scene where she tells Tlotoxl there is nothing he can do? It is so good - Barbara, you are so bad-ass I love it)
It is far from the last time in the show’s history that anyone attempts to change a society for what they consider to be the better; it isn’t even the first time in the show’s short run. The reason it becomes a problem this time is that this is that they are interfering with our history.
It doesn’t matter as much when the Thalis are prompted to attack the Daleks, because we don’t live on Skaro, nor is it an issue hanging out with Marco Polo if you are just trying to leave - but actively trying to change something that can be found in a text book? That is when the Doctor has to say no.
Personally, I’m going to miss these historical adventures once they are gone, but you can already see why - Doctor Who can’t sustain itself as a show about non-interference, and The TARDIS crew can only stand on the sidelines of Earth history for so long. The show is still figuring out it’s own rules, and they are realizing look but don’t touch isn’t any fun.