Bonnie, the leader of a splinter group of shapeshifting Zygons, has taken Clara’s form (Jenna Coleman), stashing her body in a pod. Clara finds herself dreaming of being in her flat but is able to control Bonnie’s actions slightly because of the telepathic connection between them. This gives the Doctor (Peter Capaldi) and Osgoode (Ingrid Oliver) a chance to bail out of their plane before Bonnie destroys it with a missile.

They land on a beach. Able to control Bonnie’s hand somewhat, Clara sends a message to his phone, saying, “I’m awake.” The Doctor calls Bonnie on video and, with winks, Clara tells him her pod is in London. But Bonnie is able to read Clara as well and learns that the Osgood Box is in the UNIT Black Archive under the Tower of London. Bonnie wants to seize it and unmask 20 million hidden Zygons on Earth, starting a war. UNIT leader Kate Stewart (Jemma Redgrave) has escaped Zygon control in New Mexico, reconnecting with the Doctor and Osgood in London.

Bonnie finds that there are two Osgoode boxes, in two different colours. The Doctor, Osgood, and Kate arrive, but Bonnie has already found that there are two buttons inside each box. Bonnie prepares to press a button in the blue box that will either unmask the Zygons or make their human forms permanent. Kate prepares to do the same with the red box, which will either destroy every Zygon or destroy every human in London. The Doctor tries to talk them out of this. Only the drastic consequences have kept the peace. In an impassioned speech, he asks that if they win and have their utopia, what will they do with the next bunch of rebels? Have another war? How many people will die before the do what they should have done in the first place—sit down and talk?

After the Doctor speaks of living with the consequences of the Time War, Bonnie and Kate both back off. Bonnie realizes the boxes are empty. The Doctor wipes Kate’s memories to keep the peace treaty in force. Bonnie calls off her insurrection. Later, the Doctor offers Osgoode a chance to ride in the TARDIS, but she refuses. Bonnie has given up Clara’s appearance and takes on that of the other Osgood.

The Doctor says he once had a box with a button and almost used it as a Time Lord Doomsday Device in the Time War. The Doctor’s parachute has a Union Jack pattern, like that of James Bond in The Spy Who Loved Me. The episode was praised for its ant-war message and for the acting of Peter Capaldi and Jenna Coleman. The Doctor says his first name is Basil, but we shouldn’t believe it. Actress Ingrid Oliver, who played both Osgoods. Claims to have chosen which of them was killed and then remade but has not revealed which.