The Doctor (William Hartnell), Ian (William Russell), Barbara (Jacqueline Hill) and Susan (Carol Ann Ford) find themselves stranded in Aztec times when the TARDIS is trapped in a tomb. Proclaimed a goddess by the Aztec priests, Barbara attempts to change the course of history by forbidding the human sacrifices which are part of the Aztecs' religion. It is up to the Doctor to find a way back into the tomb and recover the TARDIS, before the priest Tlotoxl (John Ringham) unmasks Barbara.