In the Prologue, the Doctor (Peter Capaldi) returns to the planet Karn. There, Ohila of the Sisterhood (Clare Higgins) explains that someone is searching for him across time and space. In the second prologue—The Doctor’s Meditation—the Doctor appears in medieval times alongside Bors (Daniel Hoffmann-Gill), apparently a loyal friend who questions who he must face and is it an old friend or a foe. The Doctor doesn’t know.

The Doctor, travelling in a war-ravaged landscape, finds a young boy (Joey Price) trapped in a field of landmines—or more precisely, hand-mines, because they are human hands reaching up from the ground. He tosses his sonic screwdriver to the boy so he can communicate and save himself, until he learns that the boy is Davros, the future creator of the Daleks, and then the Doctor abandons him.

On present-day Earth, all the airplanes are frozen in mid-flight. Clara (Jenna Coleman) is called to UNIT Headquarters to contact the Doctor. While there, they are contacted by Missy (Michelle Gomez), who wants to speak to Clara. It was Missy who stopped the planes to get attention. In a café, she asks Clara for help speaking to the Doctor, as she has received his last will and testament—called a Confession Dial—and thinks he may be dying or considering suicide. They track him down to Essex in 1138.

Clara and Missy find him partying. A character called Colony Sarff—a being made of numerous snakes who is an agent of Davros—tells the Doctor that Davros is dying. He gives the Doctor the sonic screwdriver. Feeling ashamed for abandoning the boy all those years ago, he agrees to be taken away. Missy and Clara insist on coming along. As they leave, Bors is revealed to be a Dalek puppet and steals the TARDIS.

Sarff takes them to a space station and the Doctor appears before Davros (Julian Bleach), who shames the Doctor. Missy is suspicious and shows Clara that the station is an illusion. They are actually on the planet Skaro. They are captured by Daleks and taken to the room containing the TARDIS. The Doctor pleads for their lives, but Davros claims he has no control over the Daleks. Missy, Clara, and the TARDIS appear to have been destroyed. Davros insists the Doctor confess that compassion is wrong. On the battleground, the Doctor speaks to the young Davros again, pulls out a Dalek weapon, and vows to save his friend.

In the Moldovarian Bar, Doctor Who’s answer to the Mos Eisley Cantina, which appeared in A Good Man Goes to War, are a Sycorax, the Hath, an Ood, and a Tivolian. Also, the Shadow Proclamation and a Judoon. The Sisterhood of Karn comes from the Tom Baker story The Brain of Morbius. There are scenes from a number of Davros stories of the past, and several different Dalek designs. The Doctor plays the electric guitar for the Medieval people, like in the Bill and Ted movies, and when Clara and Missy show up, he plays Oh, Pretty Woman, by Roy Orbison. Peter Capaldi was the guitarist in a band with Craig Ferguson, called the Dreamboys. The episode received critical acclaim, as full of wit and menace.