In the alien dimension called Kasaavins, the Doctor meets the 19th Century computer pioneer Ada Lovelace (Sylvia Briggs), who taking the Doctor’s hand, is transported with her to an invention exhibition in 1834, where the Master turns up. The Doctor realizes that the Master knows the aliens’ intentions but does not understand them. Ada takes her to see polymath Charles Babbage (Mark Dexter), where the Doctor summons a Kasaavin alien, hoping to be returned to the 21st Century. Ada grabs her hand and they end up in Paris during World War II. They are rescued by British spy Noor Inayat Khan (Aurora Marion) and the Master pursues them as a Nazi Officer. The Doctor meets the Master at the top of the Eiffel Tower, where he reveals that the Kasaavins were killing for him and says that Gallifrey has been destroyed. The Doctor manages to ruin his disguise and the Nazis turn on him. The good guys return to the present in the TARDIS.
Ryan finds that the Doctor has created instructions on landing the plane safely. They do land safely, but Barton has labelled them persons of interest and there is a worldwide manhunt for them. But they manage to steal one of Barton’s cars and go to a warehouse housing a Kasaavin figurine. The Kasaavins intend to rewrite human DNA. The Master had to take the long way around without his TARDIS and finally arrives in the 21st Century but finds his figurine failing because the Doctor has put a virus in it. The Kasaavins are falling back into their own dimension and take the Master with them, but Barton escapes.
The Doctor goes back in time and leaves instructions for the companions to survive the plane-crash. Then she returns Ada and Noor to their own timelines and erases their memories of her. She visits the ruins of Gallifrey and finds a message from the Master confessing to destroying the Time Lords because he realized that Time is a lie because of “The Timeless Child.” The companions force her to tell them some of her backstory.
Both episodes were written by showrunner Chris Chibnall. Part One was directed by Jamie Magnus Stone and Part Two by Lee Haven Jones. Part One was dedicated to long-time scriptwriter Terrance Dicks, creator of The Master, who died in 2018. The two parter was generally positively reviewed by critics. By and large, the Bondian spoof was liked by audiences. Stephen Fry as head of MI-6 was a hoot. The Doctor has a new outfit for her second season, but she is confronting the traditional Doctor Who villains—first the Daleks, then the Master.