The TARDIS materialises inside the tomb of Aztec High Priest Yetaxa. The Doctor and his companions are separated from the TARDIS when they manage to leave the tomb. Autloc, the High Priest of Knowledge, proclaims Barbara as the divine reincarnation of Yetaxa as she is wearing a bracelet she found inside the tomb.
Barbara attempts to use her new-found status to put an end to the violence of the period, and to put a stop to the sacrifices. Ian is made Chief of the Aztec Warriors, and finds himself in competition with the Chosen Leader, Ixta.
The Doctor becomes close to an Aztec Lady, Cemeca, whilst Susan becomes a handmaiden, but causes a rumpus when she turns down the final wish of marriage of the Perfect Vitcim.
Barbara, in her attempts to alter history, is found to be a fake, and Tlotoxl wins the day. The Doctor manages to reopen the tomb using a pulley system, and they manage to return to the TARDIS.