Parts: 4
Writer: John Lucarotti
Airdates: 23 May 1964 - 13 June 1964
Production Code: F

Episode Titles: The Temple of Evil; The Warriors of Death; The Bride of Sacrifice; The Day of Darkness

Doctor: first
Companions: Susan, Ian, Barbara

Story: Barbara is immediately intrigued when the TARDIS lands in an Aztec tomb around 1430. As she and Susan examine the remains of a priestess, Barbara absentmindedly slips a serpent bracelet which she had been examining onto her wrist. Susan finds that part of the wall swings open, and when she returns to the TARDIS, Barbara goes outside. The panel closes, shutting Barbara out, where she is found by a group of Aztecs.

When the Doctor, Ian and Susan also exit the tomb, they discover that when the wall swings shut behind them, there is no way to get it to open again. Unable to reach the TARDIS, they befriend Autloc, the High Priest of Knowledge, who thinks they are the servants of Yetaxa. Apparently, having seen the bracelet on her wrist, the Aztecs believe Barbara to be the reincarnation of the priest in whose tomb the TARDIS arrived.

But while Barbara's godlike status gives her a certain amount of freedom, it also brings a great amount of responsibility. Knowing from her studies about the violent history of the Aztecs, Barbara determines that she will try her hardest to alter history and stop the barbaric practice of human sacrifice, despite the Doctor's insistence that such tampering is impossible. But with her actions arousing the suspicions of Tlotoxl, the dangerous High Priest of Sacrifice, Barbara must walk a fine line between trying to make a difference and keeping herself and her friends from a bloody death at the hands of the enraged Aztecs.