Doctor Who: The Aztecs (1964) written by John Lucarotti and directed by John Crockett
First Doctor William Hartnell lands the TARDIS in 16th century Mexico. The Spanish Conquistadors have not yet arrived and the Aztec culture is in full development. Except that there's been a drought and the people are hoping for the gods to save them. High Priest of Sacrifice Tlotoxl is ready to perform a human sacrifice (a common thing in Aztec culture) to bring back the rain. The TARDIS lands inside a temple and companion Barbara (the school teacher whose expertise is history) is the first one out. She is mistaken for a reincarnation of their god Yetaxa. She not only thinks it will be good fun to be divine, she also plans to end the evil parts of Aztec culture so that when the Conquistadors do come, they won't wipe out the Aztec civilization.
The Doctor (who is mistaken for her servant) strongly objects to altering history, saying it is impossible. Barbara insists on trying, which arouses the suspicions of Tlotoxl. Another high priest, Autloc, is the High Priest of Knowledge and more willing to change their customs. Barbara is encouraged by his reaction but as the story goes on, it's clear that Autloc is the odd man out and Tlotoxl represents the views of most Aztecs. Since the TARDIS is stuck behind a one-way door in the temple, the Doctor and his companions can't just run away immediately, making their stay longer and more perilous than they would like.
The show is a fascinating look at and discussion of pre-Columbia Aztec culture. While clearly condemning the abominable evil that went on, the show walks a fine line in presenting the barbarity of the culture while showing that not every aspect of the culture was evil. The supporting characters (even the villains) are well-developed and understandable if not always sympathetic.
The show also benefits from the high production values. The sets and costumes look great and the actors all give fine performances. The bad guys don't chew the scenery and no rubber-suited aliens are on display. One or two fight sequences are slow and unexciting. The cliff-hangers for the four parts of the story all work well.