The Doctor arrives at the headquarters of UNIT, a team tasked with handling extraterrestrial threats on Earth, and meets with their leader Kate Lethbridge-Stewart and other members.

After they leave, Mrs Flood suddenly treats Cherry with contempt and observes an incoming storm, stating "he waits no more".

[4] Some of these storylines also continued to explore plot threads surrounding the Timeless Child, which previous showrunner Chris Chibnall introduced during his era.

[9] He was also revealed to be "the one who waits", mentioned to the Doctor by the Toymaker in "The Giggle" (2023), and the leader of the Gods of Chaos, another member of which was encountered in "The Devil's Chord" (2024).

[12][13] "The Legend of Ruby Sunday" was directed by Jamie Donoughue, who compared the two-part finale to a feature film.

[15][16] To create the scene of the TARDIS crashing into the UNIT headquarters, a tennis ball was rolled down the aisle on the set to allow for interaction with the performers.

[17][18] Millennium FX designed the mask for Twist's character with the goal of accentuating her bone structure without suggesting the appearance of a zombie.

Jemma Redgrave reprised her role as Kate Lethbridge-Stewart,[20] while Bonnie Langford guest-starred as former Sixth and Seventh Doctor companion Mel Bush.

[29] References to "Triad Technology" had been planted in Doctor Who as early as "The Giggle", where the company was mentioned in dialogue,[30] as well as "The Church on Ruby Road", where a fictional advertisement appeared on a bus.

These included a nanny pushing a stroller in 1946 Pennsylvania, a blue-skinned extraterrestrial working in an alien diner as a waitress who would have served the Doctor and Ruby, and a "human astronaut addressing a colony of giant ants".

Other returning cast members include Alexander Devrient, Michelle Greenidge, Anita Dobson, Angela Wynter, and Aidan Cook.

Rush was originally cast to voice the character Eric in the series opening episode, "Space Babies".

[36] The remainder of the guest cast included Genesis Lynea, Fela Lufadeju, Tachia Newall, and Jasmine Bayes.

[45] The episode was shown the following week in select cinemas in the United Kingdom alongside the series finale "Empire of Death".

[49] David Opie of GamesRadar+ praised the Time Window sequence and Langford's and Gatwa's performances together, though he felt the character of Ruby was underused in the episode.

[50] The New York Times author Isobel Lewis applauded Davies' writing and the programme's increased production value, stating that it was "such a bone-chilling adventure — one far scarier, far more ambitious, than I expected from the show’s Disney era.

[53] Benji Wilson of The Daily Telegraph gave the episode two out of five, criticising the special effects of the "amorphous dust cloud" and the use of the supporting cast.