Mandip Gill and John Bishop, who portray the Doctor's companions, Yasmin Khan and Dan Lewis, also depart.

Janet Fielding and Sophie Aldred respectively star as Tegan Jovanka and Ace, former companions of the Doctor.

The episode sees a number of previous series regulars and recurring cast members make guest appearances.

The Thirteenth Doctor and her companions intervene in a CyberMaster attack on a bullet train, but are unable to stop them from escaping with a child.

The Doctor's former companions Tegan and Ace investigate the abduction of seismologists and the addition of Rasputin's face to famous paintings.

The Doctor learns the Master and his CyberMasters have allied with the Daleks to trigger simultaneous volcanic eruptions across Earth.

Under arrest at UNIT headquarters, the Master uses a miniaturised Cyberman as a Russian doll, bringing in a large number of Cybermen which free him.

The Doctor encounters mental manifestations of some of her past incarnations, who inform her it may be possible to undo the forced regeneration.

It is the final story in a trio of specials that also comprised the seventh and eighth episodes commissioned for the thirteenth series.

The incoming and returning showrunner, Russell T Davies, penned the episode's final moments, continuing a trend he had started.

[16] Davies explained this by saying that having a heterosexual man appear in woman's clothing "can look like mockery", especially when the physical differences between Tennant and his predecessor were taken into account.

[18][19] Also starring in the episode are Janet Fielding and Sophie Aldred who returned to the programme as former companions Tegan Jovanka and Ace.

[22] On their return, Chibnall said he believed Fielding and Aldred's original eras to be representative of specific times in Doctor Who's history.

"[25] McCoy felt very emotional about his return and was glad to finally give closure to the Seventh Doctor and Ace.

Chibnall did not ask Christopher Eccleston, Matt Smith or Peter Capaldi as he wanted the focus on the classic Doctors.

Dhawan played the latest incarnation of the Master and Patrick O'Kane portrayed Ashad, both of whom first appeared in the twelfth series.

The remainder of the guest cast included Richard Dempsey, Anna Andresen, Sanchia McCormack, Joe Sims, Danielle Bjelic, and Jos Slovick.

[35] Former companions Ian Chesterton, Jo Jones and Mel Bush, portrayed by William Russell, Katy Manning and Bonnie Langford, respectively, appear in brief cameos near the end of the episode.

[29] In an interview with Doctor Who Magazine Langford described her appearance in the episode as being "last minute" and was pleased with the fan reception to the scene.

[37] Chibnall's original script included the possibility of other returning companions, such as Martha Jones, Ryan Sinclair, and Jackie Tyler.

[12] Among the musical cues heard in the episode is "Rasputin" by Germany-based pop and Eurodisco group Boney M. which was originally released in 1978.

After the episode's broadcast, they expressed concern that it would encourage viewers to place themselves in danger as well as add a burden to their employees and emergency rescue services.

[47][48] Tennant's portion of the regeneration was filmed on a green screen on 13 May 2022 at Bad Wolf Studios, where sound stages had since relocated.

[53] Gabriel Tate of Metro shared similar sentiments, writing that he appreciated the numerous past references.