In this serial, Barbara becomes a goddess, which changes exactly nothing about her, except making her even more awesome than she was before.
ALL GLORY TO THE HYPNOBARBARA
This is one of my favorite serials, simply because it gave Jacqueline Hill a chance to show off her acting skills so thoroughly, metamorphosing from a down to earth, sensible school teacher to a haughty deity. The TARDIS lands the crew in a tomb in 15th century Mexico. Barbara, being a history teacher, geeks out, puts on a shiny bracelet, and is mistaken for the incarnation of a deity by the local priests. Despite the Doctor’s numerous warnings about trying to change history, Barbara sets about to stop human sacrifice and save the Aztec civilization from their inevitable destruction. Meanwhile, Ian has to fight an Aztec warrior, Susan is going to be forced into an arranged marriage, and the Doctor accidentally gets engaged.
This serial sets up the idea of not altering history, a recurring theme in Doctor Who. Barbara’s intentions are good, but her attempts nearly get her friends killed, embroil her in political machinations, and end in a good man exiling himself from society, having had his faith greatly shaken.
As far as characterization goes, we see the Doctor soften up a bit more (he shows some regrets at actually having to leave his accidental fiancé, as she is a kind and intelligent woman), Barbara’s more fallible side (she wields her power like a hammer at times), and Ian’s fighting skills (the man beats an Aztec warrior twice).
Overall it is quite bittersweet, as the serial ends with the characters lamenting that that the Aztecs will be destroyed despite their scientific advances.