TARDIS in an attempt to return to 1963. Barbara remains level-headed and logical, allowing the Doctor to trace the source of the distress to telepathic influences from the TARDIS (which is trying to warn them of a major failure). Seeing that Barbara has been hurt by his accusations, the Doctor apologises and begins to realise he can rely on the two teachers, sealing a friendship which lasts until their eventual departure from the TARDIS. Although mutually respectful and increasingly affectionate, the relationship between the Doctor and Barbara is often tested by their opposing viewpoints. In The Aztecs, Barbara is mistaken for the reincarnation of a high priest, Yetaxa, after they find her in possession of his bracelet. Barbara seizes this opportunity to change the course of history, and tries to persuade the Aztecs to abandon human sacrifice, so that by the time Hernán Cortés – who overthrew the Aztec empire – lands he will find a glorious civilisation. The Doctor warns Barbara that she cannot rewrite history, but his protests fall on deaf ears. Barbara fails and, although she has influenced some Aztecs, history remains on course. Angry at Ian, the Doctor tries to take him and Barbara home, but in The Reign of Terror they end up in the French Revolution, where Barbara and Susan are captured and nearly guillotined. In the second season opener, Planet of Giants (1964), the TARDIS crew are miniaturised and Barbara becomes infected by a deadly insecticide. Barbara sees the departure of Susan and aids in the rescue of the abandoned orphan Vicki (Maureen O'Brien), who takes Susan's place on the TARDIS. In the subsequent adventure, The Romans, Barbara is sold off as a slave and ends up as a servant in Nero's palace; due to his interest in her, Nero's wife Poppaea tries to poison her. Barbara and Ian leave in The Chase (1965). After the Daleks who have been pursuing the TARDIS have been destroyed, Barbara suggests to Ian they use the abandoned Dalek time machine to get home. The Doctor is furious and tries to persuade them to stay with him by suggesting the journey might kill them, but the two teachers had made up their minds. After an emotional farewell to the Doctor and Vicki, Barbara and Ian are returned to London, albeit two years after their disappearance. Back on the TARDIS, the Doctor uses the time-space visualiser to check