Doctor: Jodie Whittaker
Jacob Anderson - Vinder
Thaddea Graham – Bel
Nadia Albina - Diane
Craige Els - Karvanista
Jemma Redgrave – Kate Stewart
Kevin McNally – Professor Jericho
Rochenda Sandall – Azure
Sam Spruell – Swarm
Craig Parkinson - Grand Serpent
Steve Oram – Joseph Williamson
Annabel Scholey - Claire Brown
Jonathan Watson – Sontaran Commander Stenck
Simon Carew – Ood
Silas Carson – Voice of the Ood
Nicholas Briggs - Voice of the Daleks/Cybermen
Directed by Azhur Saleem
Written by Chris Chibnall
Script editors: Caroline Buckley, Rebecca Roughan
Produced by Pete Levy
Executive producer(s): Chris Chibnall, Matt Strevens, Nikki Wilson
Incidental music composer: Segun Akinola
Running time: 6th of 6-part story, 59 minutes
First broadcast 5 December 2021
The Doctor runs from Swarm, taking Tecteun's Ood with her. Swarm and Azure advance on the Doctor but the Doctor takes off her conversion plate just as Swarm touches her, causing her to be split into three parts between various locations: the Divison spacecraft, Karvanista's ship, and the Liverpool tunnels.
On the Division spacecraft, Azure attenpts to return the Doctor's missing memories to her. The Doctor refuses to see them. Azure reveals their intent to sabotage the Flux into a time loop of universal destruction. The Ood attempts to slow down the Flux.
In the Passenger, Vinder and Diane disrupt its internal systems and escape, but are stranded in another unknown environment.
Yaz, Dan, Jericho, and Williamson take out the Sontaran vanguard with lightning from one of the tunnel doors before traveling to the present through another. They meet Kate Stewart who is leading a resistance against the Sontaran invasion. Having discovered Sontarans' weakness for chocolate, the Doctor bargains for two human psychic operatives, Claire and Jericho, to help them find the coordinates for the final Flux event to reach Earth. She takes her TARDIS from Kate.
The Doctor crashes Karvanista's ship away from the shield formation into the Dark Energy Camera in Chile, the Sontaran top outpost. They are stopped by a force field, captured, and placed on one of the Sontaran ships, Karvanista reveals to the Doctor that during her time in the Division, he was her companion. He cannot say more about it as the Division implanted a poison in his brain that would kill him if he spoke of their time together. The Sontarans apprehend the Doctor and inform Karvanista of the Lupari's genocide.
The Doctor piloting the TARDIS frees her captured self from interrogation and traps the Grand Serpent in his own torture device.
Bel downloads video transmissions of the Sontarans offering alliance with the Cybermen and Daleks, a ruse to sacrifice them to slow the Flux, thus vanquishing their enemies while they remain safe behind the Lupari shield. Claire escapes the Sontaran ship. Jericho cannot. The Doctor rescues Vinder and Diane, who joyously reunite with Bel and Dan. The Doctor reforms the Lupari shield behind the Sontarans instead of in front, leaving the Flux to consume the Sontarans, Jericho, Daleks and Cybermen. Some of the Flux makes it past the shield, so the Doctor uses the Passenger, a repository of endless matter, to absorb it.
Azure and Swarm bring the Doctor to Atropos to sacrifice her to Time, but since the Flux failed to free Time, Time destroys them. Time lets the Doctor go but warns that the end is coming for her before reunifying her. In the tunnels, Kate and Vinder strand the Serpent on a small asteroid through one door. Vinder and Bel decide to travel with Karvanista. Dan invites Diane to go for a drink with him, but Diane, due to her experiences, refuses. The Doctor invites Dan to join her and Yaz on their travels. She deposits the fob watch containing her lost memories into the TARDIS interior, telling it to hide it until she really asks for it.