For the time being they are safe because they are believed to be the servants of Yetaxa. If they are found out, they will be used as human sacrifice. Barbara is a history teacher, who specialised in the Aztecs - for her, this false pretence is the perfect opportunity to save the Aztec civilisation from Cortes by ending human sacrifice forever, but the Doctor strongly advises her not to interfere in history.
Ian must struggle with Ixta for the right to command the Aztec Warriors; Susan is sent to a seminary to learn Aztec culture; and the Doctor spends his time in a garden for the elderly, where he seeks to discover a way back into the tomb and where he is assisted by the lady Cameca.
But they must act quickly, for the Priest of Sacrifice Tlotoxl knows Barbara to be a fake. It is a question of time as to how long she can play Autloc off against Tlotoxl.
They escape by making a wheel and pully to open the tomb door during a sacrifice. Ixta is killed fighting Ian, Autloc loses his faith and wanders into the wilderness, and Tlotoxl consolidates his power. The Doctor reassures Barbara that she didn't save a civilisation, but she saved one man: Autloc.
I am in no doubt - this is one of my absolute favourites, and I am not alone in that! This story, like Marco Polo, was written by John Lucarotti.
The incidental music is excellent and at times very atmospheric. The costumes are spot on. And the cast are simply superb. Jacqueline Hill puts in another brilliant performance as Barbara and, proving that villains are often the best characters, John Ringham is suitably cunning and evil as Tlotoxl. The latter delivers his dialogue, like some of the other supporting cast, in a somewhat Shakespearian manner which adds to the story, not detracts.
There are two truly brilliant scenes in this. The first is when the Doctor makes cocoa for himself and Cameca only to discover, to his horror, that this means he is engaged to her!
The second is the discussion between Barbara and the Doctor
Barbara : "Oh, don't you see? If I could start the destruction of everything that's evil here, then everything that's good will survive when Cortes lands."
The Doctor : "But you can't rewrite history! Not one line! Barbara, one last appeal: what you are trying to do is utterly impossible. I know! Believe me, I know!"
Barbara: "Not Barbara...Yetaxa."
This is the first time the show deals with that classic conundrum of time-travel: if you can go back in time, can you kill Hitler and prevent the War and the Holocaust?.
Only the role played by Cortes can be deemed a let down. Cortes was part of the colonisation and Imperialism that was to mark the development of Capitalism. So it wouldn't have mattered one jot if the Aztecs didn't have human sacrifice.
the Aztecs BBC website