Doctor: Jodie Whittaker
Kevin McNally – Professor Jericho
Barbara Flynn – Tecteun
Craig Parkinson – Prentis/Grand Serpent
Robert Bathurst – Farquhar
Craige Els – Karvanista
Thaddea Graham – Bel
Jacob Anderson – Vinder
Sam Spruell – Swarm
Rochenda Sandall – Azure
Nadia Albina – Diane
Nicholas Blane – Millington
Steve Oram – Joseph Williamson
Jemma Redgrave – Kate Stewart
Jonathan Watson – Sontaran Commander Stenck
Barbara Fadden – Weeping Angel
Isla Moody – Weeping Angel
Lowri Brown – Weeping Angel
Simon Carew – Ood
Silas Carson – Voice of the Ood
Guy List – Waiter
Jonny Mathers – Passenger
Nicholas Courtney – Alastair Lethbridge-Stewart
Kammy Darweish – Kumar
George Caple – Alfie
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 -- 5th of 6-part story, 50 minutes
First broadcast 28 November 2021
The Doctor is transported by the Weeping Angels to a Division spacecraft. There she finds Awsok from "Once, Upon Time", who is ordering an Ood to create a final Flux event. Awsok, who is in charge of Division, explains its involvement in the development of the universe, intervening as they saw fit. The spacecraft is travelling to another universe, as a "seed vault" containing remnants of our universe. Awsok blames the Doctor for the destruction of the current universe because the Doctor defected and interfered with Division's work. Thus, Division engineered the Flux to destroy our universe. Awsok reveals herself to be Tecteun, the woman who found the young Doctor by a wormhole and raised her as a Time Lord. The Doctor blames Tecteun for taking her and robbing her of a life that could have been, but Tecteun counters that the Doctor does the same when she brings companions along on her adventures.
Dan, Yaz, and Jericho travel around the world in 1904 to try to discover when the end of the world will come, evading countless assassins. A prophecy from a hermit in Nepal suggests they should reunite with Karvanista; although they are able to leave a message for him at the Great Wall of China, he does not have the use of time travel so cannot respond. Their travels subsequently lead them to Joseph Williamson and the mysterious tunnels he dug under Liverpool. Williamson had discovered in his excavation several doorways that lead to various time periods and locations.
In 1958, the Grand Serpent, going by Prentis, is asked to help form UNIT by a general. Using time travel, he embeds himself into UNIT's operations and leadership over the following decades, eliminating those who pose a threat to him. In 2017, when Prentis closes the taskforce down Kate Stewart realises his deception and threatens to expose him. After a failed assassination attempt at her home, she goes into hiding. With UNIT eliminated, in 2021 Prentis orders the lowering of Earth's defences and deployment of missiles upon cities, clearing the way for a second Sontaran invasion.
When a Lupari ship breaks Earth's shield, Karvanista recalls the missing Lupari ship of the fleet which was stolen by Bel, disrupting her plan to travel to the source of the Passenger signal. With Karvanista on board, Bel's ship is attacked by Sontaran forces. Vinder also pursues the Passenger signal, arriving too late to see Bel but finding those who were taken being disintegrated by Swarm and Azure for use as a power source. He is caught by Swarm and captured in a Passenger, where he meets Diane.
Swarm and Azure follow the Doctor to the Division spacecraft and plan on exacting revenge upon Division who had imprisoned them. Swarm disintegrates Tecteun and approaches the Doctor to do the same.