In this installment of the classic series, time traveler Doctor Who (William Hartnell) -- along with his granddaughter (Carol Ann Ford) and schoolteachers Barbara Wright (Jacqueline Hill) and Ian Chesterton (William Russell) -- find themselves amid Mexico's 15th-century Aztec population. When the natives mistake Barbara for a reincarnated priestess, the quartet gets swept up in a potentially lethal power struggle.