The Borad plans to genetically alter Peri.

The Borad intends to destroy the people of Karfel.

The crew venture out of the Tardis into 15th Century Mexico and the tomb of the Aztec High Priest Yetaxa. When Barbara stumbles upon the Aztecs they mistake her for a reincarnation of the High Priest himself.

Barbara's interference in the Aztec practice of human sacrifice casts doubt over her supposed divinity and puts the whole crew in jeopardy.

It is the day of the solar eclipse when Susan is to be punished for her refusal to marry. The Doctor and his companions try to escape before they are sacrificed to the Sun God.

While in Victorian-era London investigating oddities such as spontaneous combustions and a dinosaur in the Thames, Clara struggles to know the man the Doctor has become.

The Doctor and Sarah transport to Exxilon outside a city that seems to live like an organism. Soon after, the Doctor realizes he must find an elusive antidote to defeat a galactic plague spread by the Daleks.

Since the planet Exxilon is futile because of an energy drain leaving TARDIS without power, the Doctor is forced to look for the antidote to a galactic plague. To make matters worse, the Daleks--the creators of the plague--have arrived.

On Exxilon, a war rages between two factions caging the Doctor and Sarah in the middle. Aided by rebel leader Bellal, the Doctor and Sarah continue their perilous search for the cure to neutralize an imminent plague.

An unstable alliance between the humans and Daleks results from their common goal of destroying the 'living city.' Despite their intentions the Doctor has a much safer solution, spoiling the Daleks plan to unleash an apocalyptic plague.