In the episode, the Fifteenth Doctor (Ncuti Gatwa) and his companion, Ruby Sunday (Millie Gibson), attempt to save the city of Finetime from human-eating slugs, primarily by communicating with Lindy Pepper-Bean (Callie Cooke) through social media.

The episode features themes of the effects of social media on society, racism, and elitism and has been compared by Davies and critics to the anthology series Black Mirror.

Lindy Pepper-Bean lives in the city of Finetime, populated by white, wealthy young adults from nearby Homeworld and shielded from the dangerous Wild Woods surrounding it.

They live through a social media interface, a literal bubble projected around their heads by floating "Dots", robots that also direct their movements.

When Lindy is cornered, she reveals Ricky's birth name was Richard Coombes (C preceding P in the English alphabet), and abandons him to be killed by the Dot.

The Doctor offers to take Lindy and the other remaining survivors into the TARDIS to find them a new home, but they disdainfully refuse, implying that his appearance makes him inferior.

[2] Davies ultimately pitched the episode to Moffat in April 2010 for the sixth series, but it was scrapped due to the budget constraints that the heavy visual effects would have required.

The Finetime residents' rejection of the Doctor in the final scene has been widely interpreted as due to his skin colour, a notion confirmed by Davies as intentional.

[23][24] Only white actors were cast in the guest roles due to the episode's theme of racism; Davies was unsure when or if viewers would notice the lack of diversity before the final scene.

The website's consensus reads: "A withering treatment of the terminally online with slithering monsters thrown in for good measure, "Dot and Bubble" is another memorable adventure for The Doctor.

[19] Den of Geek's Stefan Mohamed wrote about comparisons between the episode and Black Mirror beyond just the plot and saying the two are also similar with their production design.

[41] Mohamed also felt that the underlying racism shown by characters in "Dot and Bubble" was the most important part of the episode but wished for such matters to be raised by a non-white writer in the future.

[10] Isobel Lewis with The New York Times furthered this point explaining that a character referred to the TARDIS as "Voodoo", which has been used as a racial slur.