Clara (Jenna Coleman) and Missy (Michelle Gomez) are outside the Dalek City. Missy used their vortex manipulators to make it seem as if they had been killed by the Daleks. But the devices did not survive. They enter the city through the sewer, which holds a number of decaying and insane Dalek mutants. They capture a Dalek and steal its casing, which Missy convinces Clara to climb into to enter the city. Clara discovers that anything she says inside it comes out as “Exterminate!” or “I am a Dalek.” Missy takes off.
The Doctor (Peter Capaldi) does not believe Clara is dead. As the Doctor confronts Davros (Julian Bleach) and the Supreme Dalek (voice of Nicholas Briggs), the Doctor is knocked unconscious by Colony Staff (Jami Reid-Quarrell). When he wakes, he finds Davros and himself attached to cables that provide life-support to the dying Davros from every Dalek. Davros tempts the Doctor to wipe out the Daleks, but the Doctor confesses he came to show compassion for Davros. The Doctor tries to give some of his regeneration energy to Davros, but it also regenerates every Dalek, creating new hybrid forms.
Missy appears. She kills Sarff and saves the Doctor. But even the insane Daleks are regenerating, and they attack the city, seeking revenge. Trying to escape, the Doctor and Missy run into Clara as a Dalek. Missy tells the Doctor that this is the Dalek who killed Clara, but the Doctor sees through the lie. He frees Clara and tells Missy to run. Missy is cornered by Daleks, but she has a plan.
Using his sonic sunglasses, the Doctor summons the TARDIS, which survived, thanks to its Hostile Action Displacement System. As the Dalek city is destroyed, the Doctor understands why the Dalek casing allowed Clara to beg for mercy, alerting the Doctor to her plight. A Dalek should not even know the concept of mercy, and he knows where the idea came from came from. He travels back to the battlefield and uses the Dalek gun to eradicate the handmines and free the boy Davros showing him mercy.
The episode did not get great numbers because it was on opposite the England-Wales Rugby match, but it received high praise from reviewers, especially Missy, who is always a hoot. The Fourth and Fifth Doctors appear briefly. The Doctor lost his original sonic screwdriver in a Fifth Doctor story The Visitation. It was replaced in the 1996 TV movie. The cyan blue Dalek is a tribute to the original Doctor Who. Davros wants to look upon the doctor with his own eyes, as the dying Anakin Skywalker wants to look at Luke. Missy tells a Dalek “The bitch is back,” quoting an Elton John song, the first time that word was used since Rose said it. We see Davros out of his chair and it’s pretty gross. This is the first time the Master has met Davros. The Doctor is the Magician, Missy is the Witch, and Clara is both the Apprentice and the Familiar.