"You can't rewrite history, not one line."

In the earliest surviving of Doctor Who's historical adventures, the TARDIS materializes in an ancient Aztec tomb. The Doctor and companions Ian, Barbara and Susan find much to admire in the Aztec civilization.

However, Barbara has been mistaken for the reincarnation of the Aztecs' high priest, Yetaxa. The time travelers soon find themselves caught up in a vicious power struggle that could cost them their lives, especially if Barbara continues to wield her influence in an effort to divert the course of history.